My wife was making a call on her iPhone 4. While navigating a phone tree on the number she called (press 2 for...)the keypad became unresponsive and then "caught up" (she could hear the beep for pressing "2" several times after pressing it with no response) and then the phone powered itself down. I cannot get it to power back on now. I've tried charging on two different chargers and the computer, holding the power button, holding both buttons, attempted to boot into DFU mode and checked the phone for any signs of dirt/damage. None of these have provided any response from the phone. Any other suggestions to power the phone back on would be greatly appreciated.