"Try Disk Utility
1. Insert the Mac OS X Install disc, then restart the computer while holding the C key.
2. When your computer finishes starting up from the disc, choose Disk Utility from the Installer menu at the top of the screen. (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.
3. Click the First Aid tab.
4. Select your Mac OS X volume.
5. Click Repair. Disk Utility checks and repairs the disk."
Then try a Safe Boot, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, reboot when it completes.
(Safe boot may stay on the gray radian for a long time, let it go, it's trying to repair the Hard Drive.)
If 10.7 or more, reboot holding CMD+r down to boot from the Restore Partition, use Disk Utility there.
You must repair the HD, if Disk Utility or fsck should fail to repair it, your best bet is DiskWarrior from Alsoft, you'll need the CD to boot from if you don't have another boot drive...
Your best bet is DiskWarrior, you need the CD/DVD though, if you don't have another Hard Drive to boot from.
But others that may work…
Intech Speedtools Pro...
The other option would be to get an External Drive, Install OSX to it & see if Migration Assistant can migrate your important info.