Home button doesn't work - tried everything, help!

Hi, I am trying to repair an iPhone 4 that a hack obviously tried first because the internals were held together by duct tape. There were literally about 3 screws holding the insides together. Anyway, the Home button is unresponsive. I tried changing the HB flex cable, and even the dock/charging port and flex cable. I've tried calibrating the home button and nothing works. Is there a remedy on the motherboard itself or is there another possible software fix that I am missing? This is a customers phone and I don't want to do a factory restore on their device. Any info or help would be much appreciated.