I was playing world at war when i was about to quit the game, my lumia 920 just freezes and then the screen goes completely black. i tried to push every button on the phone but it wont turn on. i tried pressing the low volume button+power+camera button but it just vibrates. the screen does not light up not the 3 buttons below.please help me!!!!!! im running windows phone 8.1:unhappysweat::unhappysweat::unhappysweat::unhappysweat: