SymptomsIf your computer won't start up normally, you may need to use a disk repair utility to fix the issue.
- Start from your Mac OS X Install disc: Insert the installation disc, then restart the computer while holding the C key.
When your computer finishes starting up from the disc, choose Disk Utility from the Installer menu. (In Mac OS X 10.4 or later, you must select your language first.)
Important: Do not click Continue in the first screen of the Installer. If you do, you must restart from the disc again to access Disk Utility.
- Click the First Aid tab.
- Click the disclosure triangle to the left of the hard drive icon to display the names of your hard disk volumes and partitions.
- Select your Mac OS X volume.
- Click Repair. Disk Utility checks and repairs the disk.
See this article by Apple for more information:
Resolve startup issues and perform disk maintenance with Disk Utility and fsck
If you do not have a OS X Installation disk and your Mac fails to start, you may try suggestions from this article:
How Can I Repair My Hard Drive If My Mac Won’t Start?