Reset, hold both the Home and Power buttons until the iPhone restarts itself, usually takes about 10 seconds of holding both buttons. If the Reset does not work then, Put iPhone in DFU Mode and Restore the Firmware with iTunes. DFU Mode Steps: Open iTunes on computer, connect iPhone to computer with USB Cable. Hold both Home and Power buttons for exactly 10 seconds, then release the Power button, keep holding the Home button until iTunes recognizes the iPhone in Recovery Mode, usually about 20 seconds of holding Home button. If the iPhone screen is black, blank this is DFU Mode. Click the Restore button of iTunes. If any error messages are given write them down.