If you want to restore functionality to your phone, then you need to perform a factory reset. Factory Reset wipes all the added applications, games, settings, etc., but preserves the internal storage content such as photos, music, 3rd party files, etc.
Please press Volume Up + Home + Power until the logo appears, tap on menu and Recovery will appear. Select Wipe Data/Factory Reset and wait for the phone to restart. When this operation completes, you will have a working phone restored to its factory condition.