Several times now my Desire's screen has just stayed black when pressing the power key to unlock it. It's like it's in a deep sleep with no way to wake it. If you call it the screen will not light up but the phone will either ring with no way of answering it or just flash the missed call light. The call can still be silenced or rejected with the buttons. So my question is this a hardware or software issue? I'm inclined to think software because pulling the battery then rebooting solves it, until it happens again, sometimes the same day others a few days later. I always switch the phone off at night to give it a fresh start each day. I do not use any task killers or obscure apps. Phone has minimal virgin mobile UK branding on it, and running firmware 1.15.405.4 with no option to update to the newly released version. Thanks in advance.