follow these steps: THIS WALK THROUGH IS TO HARD RESET YOUR DEVICE, YOU WILL LOOSE ALL YOUR PHONE DATA ( data stored in phone memory)
>Switch off the phone.
>Press and hold the Volume Down button and connect your charger. When you see an exclamation mark release the button.
>Now press the keys in this sequence: Volume Up. Volume Down. Power. ...
>The phone will reset and reboots.