hi,try to reinstall osx operaiting system. reinstall osx will not erase your data so give it a try.
1.if you have osx Lion 10.7, you dont need osx installation disc
2.just power on right away hold down command and R key
3.keep holding it until you see mac osx utilities screen
4.then select reinstall osx and follow the direction on the screen
after reinstalled osx, your system should be back in working order again.let me know if it workout for you. thanks