Audio Systems: internal amps, internal amps, rear seat

Question
I have a 2003 Durango and my stereo just stopped playing but has power. We replaced the stereo and still no sound. Is there a way to by pass the factory amp? We think that may be the problem HELP...

Answer
the only problem is that the infinity amplifier is off
3 reasons for that
bad fuse
bad relay turn on switch  right side of radio

or defective amplifier but this units are good and don't go bad unless you get water in it
amplifier is under rear seat