To run Repair Disk or Rebuild Premissions:
1. Insert your Mac OS X CD-ROM disc or Restore DVD disc, then restart the computer while holding the C key.
2. Once started up from CD or DVD, choose Disk Utility from the Installer menu.
Important: Do not click Continue in the first screen of the Installer. If you do, you must restart from disc to access Disk Utility.
3. Click the First Aid tab.
4. Click the disclosure triangle to the left of the hard drive icon to display the names of your hard disk volumes and partitions.
5. Select your Mac OS X volume, if necessary.
6. Click Repair.
Disk Utility checks the disk and when it's done re-choose your main drive and reboots.
As Kelly mentioned, you do not need to use the OS CD to Repair Permissions as that can be done via Applications/Utilities/Disk Utility.
To perform the fsck -y routine:
The fsck utility is run from the command line. This means that you must type a text command at a prompt (#), rather than using the mouse pointer to open an application. Examples of a CLI are the Terminal application and single-user mode. You should start up in single-user mode to use fsck.
How to start up in single-user mode:
1. Restart the computer.
2. Immediately after the startup sound, press and hold both the Command (Apple) and "S" keys on your keyboard. The computer will display a series of text messages, at which time you may release these keys.
When the computer has started up, it will display a command line prompt (#). The computer is now in single-user mode.
How to Use fsck -y From the Command Line:
Once you have reached a command line, follow these steps to use fsck:
1. At the prompt, type: fsck -y (NOTE: there is a space between the k and the -y)
2. Press Return.
The fsck utility will go through five "phases" and then return information about the disk's utilization and fragmentation. Once the check is finished, if no issue is found, you should see "** The volume <name of volume> appears to be OK."
If fsck alters, repairs, or fixes anything, it will display the message:
***** FILE SYSTEM WAS MODIFIED *****
Important: If this message appears, repeat the "fsck -y " command until this message no longer appears. It is normal for your computer to require several "passes" of fsck, because first-pass repairs may uncover additional errors.
3. When fsck reports that no problems were found, type: reboot
4. Press Return.
The computer should now start up normally and allow you to log in.
HTH
Harv