When I'm on a call my phone's screen goes off and stays off, and NONE of the buttons work - power button, volume, home, menu, back, search - nothing. The call is still going through and I can talk and hear just fine, it's that nothing else works on the phone. I can't even hang up on the call. I have to wait for the other caller to hang up first. I've installed Keepscreen, adjusted display settings, and have done a hard reset. It still behaves the same. Any ideas?