Let the phone's battery go completely dead... I mean dead to the point that the "charge battery" screen no longer appears when you press the 'home' button. (The logic here is that if the power is completely removed to the system it may reset the internal components.) I think that you're most likely going to have to take it apart but I'd try this 'no cost' possible fix first. Give it a try - nothing to lose but time at this point. Good luck!