Turn your phone off. Hold Power + volume down + back key till you see the menu come up and release the buttons. NOW BE CAREFULL. The volume up and down buttons moves the cursor up and down and the home button selects what you want to do. push down to "wipe cashe partition" hit home button,wait till its done. Move cursor back up to "reboot system now" hit home key, your phone reboots and your done.