Run Disk Utility from the Installation Disk
• Insert the Mac OS X Install/restore disc that came with your Mac, then restart the computer while holding the C
• When you see the Spinning gear, then release the C key
• Once on the Installer screen, select Utilities/Installer menu and choose Disk Utility.
• Click the First Aid tab and select the hard drive icon displaying your Macintosh HD (your hard disk's name)
• Click Repair disk and Repair Permission. Disk Utility checks and repairs the disk.
• Once completed, quit Disk Utility
• Restart your Mac.
If that didn't worked, then you have to Re-Install your Mac OS. You can do a Archive and Install
. Archive and Install will not remove any of your files,applications, settings etc. It just replaces the system files with new one.
Archive and Install : Read More
Let me know if that works or not..