I would try to clear the cache partition in recovery mode. To do this you first need to boot the phone in recovery mode.
Press the Power, Home, and Volume up buttons at the same time.
Release all key when Android or Samsung logo appear then you will see Android System Recovery.
Navigate with the volume keys, and select with the power button.
Navigate to wipe cache partition, and select it.
Wait for that to finish, then reboot your phone.
Hope that helps :)
If it doesn't work though, i would do a factory reset using the same method, unless anyone else has a better answer. (The factory reset will erase ALL personal data from your phone. So it should be a last ditch effort.)