I had a similar problem... 2001 A6 with a Symphony. Was working fine one morning. Got in the car later that day and the deck powers on but no sound from any speakers. I have pulled it and checked all cables but it is still not working. Any ideas?

 

A similar thing happened to me. Took it to a local shop and they pulled out the radio and a fuse out of the back. Popped the fuse back in and all was well.

 

just get a new one on eBay...or get an aftermarket unit

gl!