2004 Jaguar XJR -- A while back I was playing with the interface, just randomly and foolishly pressing buttons... Anyway, the entire system shut down. No radio, no climate control. I tried every and all procedures recommended to reset it, but nothing worked. Finally, I replaced the navigation unit in the trunk with one I bought used from ebay. Success! The screen is back up and I can control the climate control and the stereo, except there is no sound. Am I missing something? What do I need to do to turn the radio back on?