All of a sudden, after 3 years, the control buttons on the tv have stopped working except for the power on/off. That goes for the remote too. The tv works as a computer monitor, tv and can be switched to av for DVD player. Or I used to be able to do that. Since the buttons no longer work, I can't get to the source/menu interface screen. The channel and volume buttons do not work either. Only the power on/off button on tv and on remote will work. The tv is stuck on channel 4 which is good because I receive my cable on that channel and is able to change channels thru the cable box. This TV/monitor is no good without access to the interface menu. What is wrong?}