To find out if it's system wide or user specific, try this...
Open System Preferences>Accounts, unlock the lock, click on the little plus icon, make a new admin account, log out & into the new account.
Does it work in the new account? If not...
If 10.7 or more, reboot holding CMD+r down to boot from the Restore Partition, use Disk Utility there to repair the Disk, reinstall may be needed if errors were found.