Troubleshooting Problems with Turning Mac OS X Snow Leopard On and Off

These days, most Macs have a power-on button near the keyboard (notebooks) or the back side (iMacs). You use it to turn on your Mac, but there is a procedure for shutting down Snow Leopard properly.

When you do turn on your Macintosh, the operating system loads and OS X tests all your hardware — slots, ports, disks, random-access memory (RAM), and so on. If everything passes, you hear a pleasing musical tone and see the tasteful gray Apple logo in the middle of your screen, along with a small spinning-pinwheel cursor somewhere on the screen.


This is what you’ll see if everything is fine and dandy when you turn your Mac on.
Here are the things that might happen when you power up your Mac:

Everything is fine and dandy: Next, you might or might not see the Mac OS X snow Leopard login screen, where you enter your name and password. If you do, press Return or Enter (after you type your name and password, of course), and away you go.

The Desktop soon materializes before your eyes.


The Mac OS X Desktop after a brand-spanking-new installation of OS X.
Blue/black/gray screen of death: If any of your hardware fails when it’s tested, you might see a blue, black, or gray screen.

If your computer is under warranty, dial 1-800-SOS-APPL, and a customer-service person can tell you what to do.

Prohibitory sign (formerly known as the flashing-question-mark disk): Most users eventually encounter the prohibitory sign shown below (which replaced the flashing question-mark-on-a-disk icon and flashing folder icon back in Mac OS X Jaguar). This icon means your Mac can’t find a startup disk, hard drive, network server, or DVD-ROM containing a valid Macintosh operating system.


Kernel panic: You shouldn’t see this very often, but you might occasionally see a block of text in four languages, including English. This means that your Mac has experienced a kernel panic, the most severe type of system crash.


Turning off the power without shutting down your Mac properly is one of the worst things you can do to your poor Mac. Shutting down your Mac improperly can really mess up your hard drive, scramble the contents of your most important files, or both.

If a thunderstorm is rumbling nearby or you’re unfortunate enough to have rolling blackouts where you live, you might want to shut down your Mac.

To turn off your Mac, always use the Shut Down command on the Application menu or shut down in one of these kind-and-gentle ways:

Press the Power key once and then click the Shut Down button.

On keyboards that don’t have a Power key, press Control+Eject instead and then click the Shut Down button that appears (or press the Return key, which does the same thing).

Of course, most Mac users have broken this rule several times without anything horrible happening, but don’t be lulled into a false sense of security. Break the rules one time too many (or under the wrong circumstances), and your most important file will be toast. The only time you should turn off your Mac without shutting down properly is when your screen is frozen or when your system crashed and you’ve already tried everything else.

How to Restore OS X Lion Via the Internet

Cleaning house and cleaning out the house.
36 minutes seemed a little too good to be true. How much had Apple honestly reinstalled? I was working from a brand new MacBook Air, so certainly that must have accelerated the process. Booting back into Recovery HD, I opened Disk Utility. I repaired the disk (near-instantaneous) and permissions (4 minutes). So far so good: Everything worked as it would from a disk, only faster.

From here, I decided to reformat the Mac partition and do a fresh reinstall OS X. With no common components the process would have to be slower. Think again. Despite similar ETAs (33 minutes to the download and 38 to install) the end result was just a couple minutes longer than the previous reinstallation (39 minutes real-time). In other words, in the time it takes to watch an episode of Mad Men, I had performed a full installation of OS X over the Internet. Not bad, right?

Lion Internet Recovery, or how I learned to stop caring and love breaking OS X. 
With Recovery HD any Lion user can run Disk Utility to clean house—or clean out house—or reinstall OS X from Apple's servers. But Apple has also added a new tool called Lion Internet Recovery for the latest drive-less MacBook Air and Mac Mini.

For more OS X Lion tips, read OS X Lion: Lion-taming Tips

Let's say your Mac is totally toasted. You can't even boot into Recovery HD using the keyboard command. With Lion Internet Recovery, a new Macbook Air (or Mac Mini) can automatically connect to and boot from Apple's servers using your preferred wireless network, run a test on your hardware (memory and hard drive), and download Recovery HD so your Lion can land on its feet. Sounds great, right? The problem comes in testing it. It turns out that breaking OS X beyond repair isn't easy.

I began by booting my 11-inch MacBook Air into Target Disk Mode (Command + T) and connecting to its big brother, the 13-inch MacBook Air with a ThunderBolt cable. For simplicity's sake, hereafter I'll call my 11-inch "Li'l Mac" and the 13-inch "Big Mac."

I began by deleting the entire Library folder at the root level of Li'l Mac. How's a Mac to boot without a Library folder? It found a way. Once Li'l Mac had rebooted it began to rebuild its Library from the System Library folder. Li'l Mac: 1. Big Mac: 0.

Back on Big Mac, with Li'l Mac connected via Target Disk Mode, I deleted Li'l Mac's recreated Library folder and raised my bet: I deleted the entire System folder (90,000 odd items). I rebooted Li'l Mac. It waited 10 seconds with a gray screen and, with (seemingly) no other options available, it did the unthinkable: Li'l Mac booted to Windows from its Bootcamp partition. Li'l Mac: 2. Big Mac: 0.

Reconnected via Target Disk Mode, I used Disk Utility to format the Bootcamp partition. With Windows wiped, where was Li'l Mac to go? Rebooted, it sat on the gray screen for 20 seconds and finally opened Recovery HD. Was this Lion Internet Recovery? It wasn't, I determined, after consulting Apple's documentation. OS X still wasn't (completely) dead. Li'l Mac: 3. Big Mac: 0.

It was time for the nuclear option. On Big Mac, with Li'l Mac mounted as a disk via Target Disk Mode, I opened Disk Utility and formatted the entire drive, clearing both partitions to one clean slate. Li'l Mac had, effectively, a blank SSD. I rebooted Li'l Mac to see a blinking folder. Success. To initiate Lion Internet Recovery, I rebooted once more and held down Command + R. With literally nothing on the drive, Li'l Mac would have to beam up to Apple's servers via Wi-Fi.

And it worked. A new gray screen a spinning Earth and status appeared. Recovering Recovery HD from Apple's servers wasn't a quick process—it took nearly 45 minutes. But once it had completed, my blank Li'l Mac rebooted to Recovery HD, from which I could reinstall Lion.

No disk? No problem. 
Whether you have a new Mac with Lion Internet Recovery or you've simply installed Lion on an existing machine, Apple makes it easy to forget the disk. Reinstalling OS X from Apple's servers is quick and easy. Running maintenance through Recovery HD's Disk Utility works just as well—perhaps better—as it had from a disk. And with Internet Recovery for the MacBook Air and Mac Mini, Apple has proven that no matter how hard you try, Lion will find a way to claw its way back onto your computer. RIP DVDs. With Internet-delivered OS X, Apple makes the disk drive look like the floppy drive.

Mac Tip Of The Day #418

Apple has changed the way in which users can listen to their music even when the screen saver is running.

To be able to play your music and podcasts in screensaver mode as shown in the window above you will need to navigate to the “System Preferences” followed by “Desktop & Screen Saver.” Then make sure you are in the “Screen Saver” tab and “iTunes Artwork” is selected as shown below:

The example you see on the right hand side will be how your album artwork is displayed on the screen when the screensaver is active. Depending on how much music you have in iTunes this will change each time your Screen Saver is activated therefore allowing you a variety of options.

The options button presents the following to the user:

Rows simply indicates how many rows of album artwork will be displayed at any given time. Less rows will result in larger artwork.

The delay is set to a default of 2.0 seconds and directly relates to how frequently the album artwork will flip in the screen saver therefore presenting users with new albums to select from.

You are not able to select specific tracks using this method. You are able though to use the iTunes play/pause, next and previous buttons along with the volume up, down and mute keys on your keyboard without cancelling the screen saver. However, other keys not assigned to iTunes controls will cancel the screen saver.

In addition to this control you can also use the mouse controls to navigate between album artwork to change the album, pause a playing track or simply exit. All of these functions are represented in the image at the beginning of this article.

At present you are unable to select specific genres or playlists. You are also not able to select specific tracks or see the track information.

Mac OS X10.0: Computer With SCSI Chain Does Not Start up or Stops Responding

A computer running Mac OS X may not start up or may stop responding if the SCSI chain is improperly terminated.

Products Affected

Mac OS X 10.0

Symptom

The computer does not start up, or stops responding. The mouse pointer may appear as a spinning disc, and the computer may appear unresponsive.


Solution

This is the result of an improperly terminated SCSI chain. Verify that all SCSI chains are terminated at both ends. This includes terminating any SCSI card that is the last device in the chain.

Note: A SCSI chain that worked with Mac OS 9 may not work with Mac OS X. Mac OS 9 is more tolerant of improper termination than Mac OS X. A properly terminated SCSI chain should perform better, regardless of the version of the Mac OS.

Mac doesn't start up from disc

Symptoms

If your Mac stops responding when starting up from a Mac OS X Install DVD, learn about some troubleshooting steps you can use. 

Products Affected

Mac OS X 10.4, Mac OS installation/setup (any version), Mac OS X 10.6, Mac OS X 10.5

Resolution

Try these troubleshooting tips one at a time until you are able to start from the disc:

1. Verify that the shiny side of the disc is clean (no particles or smudges on it). Here are some tips for cleaning a disc.
    
2. Make sure you are using the disc that came with the computer, or a newer disc that contains a compatible version of Mac OS X (look at version on the label of the DVD). Please see:
   • Don't install a version of Mac OS X earlier than what came with your Mac
   • Mac OS X versions (builds) included with Intel-based Macs
      
3. To verify that your Mac is attempting to start from the disc, hold the C key as your Mac starts up. You may hear access sounds from your computer's optical drive.
   • If holding C does not help, hold the Option key during startup. Startup Manager should appear. Select your Mac OS X disc icon, then press Return.
   • If Startup Manager does not appear, make sure you are using an external Apple keyboard (directly connected), or a portable Mac's built-in keyboard. Some third-party keyboards may not be recognized in time for Startup Manager to appear.
   • If you are able to start from your hard disk, you can use Startup Disk preferences in System Preferences to select the disc, then restart.
      
4. Temporarily disconnect USB and FireWire devices connected to your computer. If you are not using a portable Mac, connect your Apple keyboard and mouse directly to your Mac. If this resolves the issue, reconnect USB and FireWire devices one a time until the issue occurs again. Once a problematice device is located, contact the manufacturer for assistance.
    
5. Your Mac may benefit from a firmware update. The latest firmware updates are available from Apple Support Downloads.
    
6. If the issue persists, shut down your Mac, then remove third-party hardware upgrades such as third-party memory (RAM) and third-party expansion cards. If this resolves the issue, contact the manufacturer of the product for assistance.

Additional Information

In rare cases, a kernel panic message may appear when you can't start from a Mac OS X disc.

Note: If you're having difficulty starting up from your hard drive, see Gray screen appears during startup instead.

Mac OS X10.0: Computer With SCSI Chain Does Not Start up or Stops Responding

A computer running Mac OS X may not start up or may stop responding if the SCSI chain is improperly terminated.

Products Affected

Mac OS X 10.0

Symptom

The computer does not start up, or stops responding. The mouse pointer may appear as a spinning disc, and the computer may appear unresponsive.


Solution

This is the result of an improperly terminated SCSI chain. Verify that all SCSI chains are terminated at both ends. This includes terminating any SCSI card that is the last device in the chain.

Note: A SCSI chain that worked with Mac OS 9 may not work with Mac OS X. Mac OS 9 is more tolerant of improper termination than Mac OS X. A properly terminated SCSI chain should perform better, regardless of the version of the Mac OS.

Mac OS X: Changing or resetting an account password

Summary

Learn how to change or reset an account password in Mac OS X, including the original administrator account password. You might need to do this when someone has lost or forgotten his or her account password.

Products Affected

Mac OS X 10.3, Mac OS X 10.2, Mac OS X 10.1, Mac OS X 10.4, Mac OS X 10.6, Mac OS X 10.5

Tip: If you forget your login password, and your home folder is protected by FileVault, see I forgot the password to my encrypted home folder.
 

Resetting a user's password

Note: These steps are for Mac OS X v10.3 or later. For information about resetting a password in Mac OS X v10.2.8 or earlier, see the Additional Information section below.

1. Log in with an administrator account. Tip: If you don't know the password of any administrator accounts, see "Resetting the original administrator account password" below.
2. From the Apple menu choose System Preferences.
3. From the View menu choose Accounts.
4. Click the lock button if it appears locked; enter the administrator password.
5. Select the username whose password you want to change.
6. Click the Reset Password button (Mac OS X v10.3 and v10.4) or the Change Password button (Mac OS X v10.5 or later).
7. Enter a new password in both the Password and Verify fields, and add a hint if desired.
8. Click the Reset Password button (Mac OS X v10.3 and v10.4) or the Change Password button (Mac OS X v10.5 or later).
9. If a dialog box appears with the message "Your Keychain password will be changed to your new account password," click OK.

Important: Passwords for administrator accounts should not be blank.

Isolating issues in Mac OS X

Symptoms

By using the approach here, you can learn how to isolate an issue to its root cause, or at minimum to determine the sequence of events that causes the issue to occur. Using this approach may help you solve the issue, locate other support articles, write better posts to Apple Discussions, or communicate with AppleCare Technical Support.

Products Affected

Mac OS X 10.0, Mac OS X 10.3, Mac OS X 10.2, Mac OS X 10.1, Mac OS X 10.4, Mac OS X 10.6, Mac OS X 10.5

Resolution

Start by asking yourself basic questions about the issue that will help you describe it:

What is the issue?

When answering this question, be sure to note any alert or "error" messages that appear. Be sure to describe any unexpected hardware or software behavior, and any other details that seem relevant.

Users accustomed to reading logs should review them in Apple System Profiler for any relevant information. If you are not experienced with reading logs, it is generally best to ignore them unless instructed to search for a specific message.

When does it occur?

• If you can identify a sequence of events that lead up to the issue, be sure to document each.
• If the issue seems to occur at certain time intervals, be sure to record the times at which it happens. Does it happen only at certain times (for example, daily at 9:00) or on a periodic basis (for example, every 47 minutes)?
• If the issue occurs so irregularly that you cannot yet describe when it happens, the suggestions below will help you troubleshoot the issue over time by making certain changes, then watching to see if the issue stops.
• If the issue occurs at startup immediately following a third-party software installation, find out what you can do.
• You can also troubleshoot any other issues that occur during startup.

If these suggestions do not resolve your issue, contact AppleCare or your nearest Apple Authorized Service Provider for assistance.

When did the issue start?

Note any recent changes to the computer and its software, since they could affect the issue. Was any new software or hardware installed?

Check documentation

After you can describe the issue, check known documentation sources, searching on key terms you have identified.

If an application program is affected, first check any "read me" files included with it. These may describe known issues.

If the issue is with a third-party product, check the manufacturer's or publisher's website for information about the issue.

Up-to-date software and firmware?

As a general rule, make sure you are using the latest versions of Apple and third-party software for best compatibility. Also make sure your computer's firmware is up-to-date.

Is it a software or hardware issue?

Pay attention to important clues.

• If the issue seems specific to a certain application or Mac OS X feature, troubleshoot software before hardware.
• If the issue occurs as the computer starts up--unless the computer does not turn on at all-- troubleshoot software before hardware.
• For other issues, or when software troubleshooting does not produce a resolution, use the rest of this document.

Use Disk Utility to check for disk errors and permission issues

Such issues can contribute to other symptoms, but are usually easy to resolve.

Can you isolate to a hardware device?

Issues with a hardware device can sometimes appear to be software issues, but are not resolved with software troubleshooting. Eliminate hardware as a cause (or conversely, isolate the issue to software):

1. Disconnect external devices. If the computer is an iBook or PowerBook computer, disconnect all external devices. For an iMac, disconnect all devices other than the Apple keyboard and mouse. For a Power Mac, disconnect all external devices other than one display (which should be connected to an original, built-in video port), and the original Apple keyboard and mouse. If this resolves the issue, add devices back one at a time (shut down first if the device requires it) to further isolate the issue.
2. Insert the Apple Hardware Test CD that came with your computer (if one did). Use the extended test. If any issues are found proceed to step 3, or contact AppleCare or your nearest Apple Authorized Service Provider to arrange for diagnostics and service as necessary.
3. Shut down the computer and remove any third-party memory upgrades, expansion cards, additional hard drives, or other internal hardware upgrades. If you are not comfortable doing this, an Apple Authorized Service provider can assist. A service fee may be charged if the issue is not related to your Apple hardware. Alternatively, you may wish to skip this step and go to "Reinstall Mac OS X" below.
   • If the issue is resolved, add your devices back one at a time. When the issue returns, remove the most recently-added device. If the issue goes away again, you have identified the cause. If software was included with the device, try deleting and reinstalling it. You may also wish to contact the vendor or manufacturer of that device for specific troubleshooting steps.
   • You may want to test devices on all available ports into which they can be used. If a USB device works on USB port 1 but not on USB port 2, try connecting other devices to port 2. It is possible that your computer's ports aren't working properly.

Reinstall Mac OS X

If an issue persists, reinstalling Mac OS X should resolve it.

• For Mac OS X v10.6, simply reinstall Mac OS X v10.6 from its installation disc.
   
• For Mac OS X v10.2, 10.3, 10.4, or 10.5, perform an Archive and Install installation.
  Tip: You won't be able to return to your previous System following an Archive and Install installation, but you can select the "Preserve existing Users & Network Settings" option to retain your original applications and settings, documents, and user accounts.
• For Mac OS X v10.1.5 or earlier, reinstallation of Mac OS X requires erasing the Mac OS X volume. This is described in the next paragraph.

If the issue persists, back up any necessary data, start up from a Mac OS X Install or Restore CD, erase the Mac OS X volume, reinstall Mac OS X and restore any additional Apple software.

Reinstall additional software one item at a time, restarting the computer after each install. For best results, use the computer for several hours after each installation to determine if that particular software contributed to the issue. Reinstalling everything at once without noting when the issue returned may lead to a need to repeat this process.

Warning: Choosing Erase and Install will completely erase the contents of the chosen volume before installing Mac OS X. Be sure to back up your files before continuing.

Mac OS X, Mac OS X Server: Changing Privileges for System Software Components May Prevent Proper Startup

A computer may not start up correctly with Mac OS X if the privileges (or "permissions") have been changed for system software components. This may occur after a change of guest user privileges.

Products Affected

Mac OS X 10.0, Mac OS X 10.3, Mac OS X 10.2, Mac OS X 10.4, Mac OS X Server 10.3

Symptom

The computer does not start up properly.

Solution

Do not change the privileges for system software components. Instead, change your share point selection.

Some people change these privileges after noticing that the guest user has rights to some system software components. However, these privileges must remain in place for the computer to start up properly.

The proper way to address this concern is to make share points from individual folders, rather than making an entire disk a share point. This approach should also prevent you from making privileges changes to the entire startup disk when using the Workgroup Manager or Server Admin application included with Mac OS X Server.

For more information, see technical document 106805, "Mac OS X: Do Not Move 'mach_kernel' or Other System-Installed Files and Folders, Some of Which Are Normally Invisible".

Mac OS X: Issues after removing "etc" and/or "var" directory alias when started up from Mac OS 9

Products Affected

Mac OS X 10.0, Mac OS X 10.3, Mac OS X 10.2, Mac OS X 10.1, Mac OS X 10.4

Aliases to the "etc" and "var" folders may be visible when started up from Mac OS 9. These aliases shouldn't be removed.

This document applies to Mac OS X 10.1.5 or later.

When starting up in Mac OS X after having been started up from Mac OS 9, one or more of these symptoms occurs:

• The computer stops responding during startup. 
• The Setup Assistant reappears. 
• BSD commands that access files in etc and var fail.
• An alert box appears with a message that contains:
  "/etc/master.passwd: no such file or directory".

Do not delete the "etc" or "var" aliases, or any other Mac OS X-installed files or folders that are visible when started up from Mac OS 9. See "Mac OS X: "Broken Folder" Icon, Prohibitory Sign, or Kernel Panic When Computer Starts Up".

If these items were deleted, use these steps:

1. Start up in single-user mode. 
2. Type: mount -uw /
3. Press Return. 
4. Type: ln -s /private/etc etc
   
   If this alert appears: "File already exists," execute the following command, then repeat the last step:
   mv /etc /private/tmp/etc.delete 
   
   
5. Press Return. 
6. Type: mv /var /var.delete
   There is a space between "/var" and "/var.delete".
   
7. Press Return.
   Tip: If you see the message "No such file or directory," make sure that the spacing and spelling are correct, then repeat the last two steps. If you still see this message after the second attempt, continue to the next step. 
8. Type: ln -s /private/var var
9. Press Return. 
10. Type: ls -l | grep ">" 
    The character before "grep" is a pipe character ("|"), which is usually located above the Return key.
    
11. Press Return.
    
    
    Look for these two items in the output:
    
    lrwxrwxr-t  1 root  admin  {date} etc -> private/etc
    lrwxrwxr-t  1 root  admin  {date} var -> private/var
    
    If any of these are not present, repeat the necessary steps above until they are.
    
    
12. Type: reboot
13. Press Return.

My Mac is showing a flashing question mark !

Don't panic...

If you see a flashing question mark when you start your Mac, it's probably because it can't find the system software it needs to start up.

Usually, all you have to do to get your Mac back up and running is remind it where its software is.

In the olden days (Pre OS X) you could drag the System File out of the System Folder and then drag it back in and it would be re 'blessed'...

After the flashing question mark appears, one of two things may happen:

The computer starts up normally after a brief delay.

The computer does not start up.

If your computer starts up normally after a brief delay, you probably just need to reselect the startup disk in Startup Disk preferences (Mac OS X) or the Startup Disk control panel (Mac OS 9).

It's normal to see the flashing question mark when a startup disk has not been selected. In most cases, reselecting the startup disk is all that is required to resolve the issue.

Check the mouse and keyboard...

If the mouse button is held down during startup, this issue might occur. Make sure the mouse button isn't pressed.

If the issue persists, disconnect the mouse and keyboard before starting up as a test. Use your computer's power button to turn it off and on. If the issue persists, reconnect the keyboard and mouse.

More solutions to try

If your computer still starts to a flashing question mark, follow the steps for your Mac OS version below.

Steps for Mac OS X 

The possible causes and solutions for this symptom appear in the order that you should try them. If any step resolves the issue, you don't need to continue to the next one.

If at any time in this process you determine that your Mac OS X system software is missing, reinstall Mac OS X.

Mac OS X system software is stored in the System and Library folders at the top (root) level of your hard disk. It is also stored in folders that are invisible when started up from Mac OS X but that are visible when started up from Mac OS 9. If you have started up from Mac OS 9 and deleted folders that were unfamiliar to you, you may have accidentally deleted your Mac OS X system software. If you're not sure, save reinstallation for your last option.


Start up from a system software CD or DVD, and repair your disk using Disk Utility:

Insert the Mac OS X Install or Restore disc.

Restart the computer, then hold the C key during startup.

From the Apple menu, choose Disk Utility. Do this in the first screen of the Installer. Don't click Continue. If you click Continue in a Mac OS X Installer version earlier than 10.2, you must restart from CD again.

Click the First Aid tab.

Click Repair Disk.

After repairing the disk, try to start from the Mac OS X hard disk.

Tip: If your hard disk is not available (mounted) when started up from CD, reset the parameter RAM (PRAM) as described in step 3, then repeat these steps.

If your hard disk is still not available after resetting PRAM, contact an Apple Authorized Service Provider or Apple Technical Support.

Try to select your Mac OS X startup disk using either Startup Manager or the X key.

If this doesn't work, go to step 3.

Reset parameter RAM (PRAM).

Reset PRAM, then see if the computer starts up. If it doesn't, repeat step 2.

If none of these steps resolved the issue, start up from the Mac OS X Installation CD and reinstall Mac OS X. If your hard disk is not available (mounted) when started up from CD, contact an Apple Authorized Service Provider or Apple Technical Support.



Steps for Mac OS 8 and Mac OS 9

The possible causes and solutions for this symptom appear in the order that you should try them. If any step resolves the issue, you don't need to continue to the next one. If at any time in this process you determine that your System Folder or its contents are missing or were intentionally deleted, reinstall Mac OS 8 or Mac OS 9.

If you normally start up from Mac OS 9 but don't have a Mac OS 9 CD that can be used as a startup disk, follow the steps for Mac OS X above. Some computers include Mac OS X Installation CDs and a Mac OS 9 Restore CD that can't be used as a startup disk. Once you've started up from Mac OS X, make sure a copy of Mac OS 9 is installed. If you erased your disk since the last time you started up in Mac OS 9, you may need to need to install Mac OS 9 drivers.

Start the computer from the Mac OS 8 or Mac OS 9 Installation or Restore CD that came with the computer.
Open the Utilities folder and locate Disk First Aid.
Open Disk First Aid and repair the disk.
Open the Startup Disk control panel.
Choose your hard disk as the startup disk.
Restart the computer.

Note: If your hard disk is not available (mounted) when started up from CD, reset the PRAM as described below, then repeat these steps. If your hard disk is still not available after resetting PRAM, contact an Apple Authorized Service Provider or Apple Technical Support.

If you can't choose your hard disk in the Startup Disk control panel, your System Folder may have been altered or removed. In some cases, you may solve the issue by moving files back into the correct location in a process known as "reblessing" the System Folder. A "blessed" System Folder is one that is recognized as a valid startup System Folder, as indicated by the appearance of the Mac OS logo badge on the System Folder.

Reblessing the System Folder only works when all the original files are still installed and in the correct location (or you can put them back in the correct location). If any files have been deleted, you may need to reinstall system software. If you have deliberately removed System Folder files, this includes putting them back where you found them.

Additionally, you should only have one folder named "System Folder" on your disk (not to be confused with the folder named simply "System" that is installed by Mac OS X, if both systems are installed on the same disk).

To rebless your System Folder:
Start up from CD.
Close any open windows.
Open the hard disk.
Choose By Name from the View menu.
Locate the System Folder. Tip: You should only have one System Folder. If necessary, rename any other "System Folder" you're not using. Don't rename "System" if Mac OS X is also installed.
Open the System Folder. At this time, you should replace any items that you have previously removed from the System Folder, if applicable.
Do one of the following:
If Mac OS X is not installed or is installed on a different volume than Mac OS 9, drag the System suitcase and the Finder to your hard disk icon. If you have more than one hard disk, drag the files to the hard disk where the System Folder is.
If Mac OS X is installed on the same volume or partition as Mac OS 9, create a new folder outside of the System Folder but on the same disk, then drag the System suitcase and the Finder to the new folder.
Close the System Folder.
Drag the System suitcase and Finder back onto the System Folder icon.

When the Mac OS logo reappears over the System Folder, it has been reblessed. Select the folder in the Startup Disk control panel, then restart the computer.

Reset parameter RAM (PRAM)

If after resetting PRAM the computer starts up normally, reselect the startup disk in the Startup Disk control panel.

Troubleshoot SCSI (if applicable)

Improper SCSI configuration, termination, or cabling may cause this symptom.

Shut down the computer.
Turn off all connected devices.
Completely disconnect the SCSI chain from your computer. If you have installed a third-party SCSI card, take it out of the computer.
Start up the computer.

If your computer starts up OK, you know something is wrong with your SCSI chain.

Check for a conflict with recently-installed software

You may be able to start up while holding the Shift key (which temporarily disables extensions). If so, troubleshoot with the Extensions Manager.

Reinstall system software

Do this only if nothing else helps.