Disconnect all peripherals from your computer.
Boot from your install disc & run Repair Disk from the utility menu. To use the Install Mac OS X disc, insert the disc, and restart your computer while holding down the C key as it starts up.
Select your language.
Once on the desktop, select Utility in the menu bar.
Select Disk Utility.
Select the disk or volume in the list of disks and volumes, and then click First Aid.
Click Repair Disk.
Restart your computer when done.
Repair permissions after you reach the desktop-http://support.apple.com/kb/HT2963 and restart your computer.
Use Software Update to update your os to 10.6.8 and anything else that needs to be updated. Repair permissions and restart your computer after the installations.
Can't repair appears. Disk utility stopped repairing Machintosh HD.
Your boot partition is messed up, hopefully you have a copy of your data on a exernal drive (TimeMachine drive might be corrupted as well)
Do this so you have a easily accessible copy of your data
Then erase the Macintosh HD parittion using the center security erase option, then quit and install OS X from Apple's servers.
You can attempt a TimeMachine restore, but if it's corrupted then you'll have to erase and install OS X fresh and return files from the storage drive or exernal boot drive.
Please tell me how install the OS X.
Once Disk Utiltiy has doen it's thing, check the partition tab and make sure Options: GUID and Format is OS X Extended Jorunaled (or make it that way)
you then quit and are back in the OS X installer, select the volume and install
Once the installer is finished, connect the external TimeMachine drive or clone.
Then quit the installer and it will reboot, Video and SetUp Assistant will allow you to re-establish the backup to the machine.
Once in you will need to Software Update fully.
If that fails then your backup data is corrupted and you will need to start over and install everything from fresh sources and only grab user files off a external drive (no TM or clone restores)
There is a bundled app installer on the 10.6 disks that can reinstall iLife, will need to run Software update fully to bring it up to date with your files.