Pioneer gone quiet!!

I've got a Pioneer DEH-P3500MP head unit, everything appears to be working on the display, CD plays etc, but no sound from speakers! Everything seems to be ok wiring wise, no wires loose or anything. Any suggestions?

Was it going and then just quit all of a sudden?
How long has it been dead like that?
How are your speakers wired up?

Make sure that none of your speaker terminals are touching anything metal. I've seen this happen twice and both times were because the speaker terminals touched metal in the door which caused a short, therefore the amp in the headunit will just cut out.

I suspect that is what has happened, i have a box in the back that i take out now and again, i think the wires touched the runners on the seat! Do you know how can i fix it? Can't be without music!!!