A long time ago I had a similar problem and most responses were to jiggle the headset. The assumption was the connection was stuck. I did that and did get sound back for short periods of time until it just died. I got a replacement phone and have not had any problems since. I know there are people here that have fixed the problem by uninstalling software but you said you did not make any software changes to the phone. For this reason it sounds like a hardware problem.