Your probably going to need to do a factory reset. the email on your registered Google account, contacts synced with google, and anything on your SD card wil be retained, but factory reset will wipe all of your apps, themas, and custom settings. Any you will have to download everything your running again but apps purchased from the marked will also be available to download again for free.
To do a factory reset turn the power off and shut down your phone, then press and hold the home key+power key+up OR down volume key.