If you could take a picture of the pcb that would help me to help you better. First thing would be to check if its power supply is working. You would have to hook up the amp in the car and turn it on. You would have to put your multimeter in vdc mode. Put the black lead of the meter on the - of the power input of the amp, and the positive on the output of the bridge rectifier. -|<|-|>|- If they are in a transitor form they may have this symbol on the front of them. If not, they may be diodes, and I'll have to get a detailed picture from you so I can point out exactly which ones they are. Put the red lead on each one of the pins, on one of them you should get a voltage >20 if its operating correctly. If its working I'll tell you what you need to do, if not it could be something else it wrong preventing it from turning on or it is in fact bad.
I should also mention that if you took the amp apart that there are often little peices of heat conductive plastic that people usually forget to put back behind the transistors. If there were some there, they MUST go back, these peices electrically insulate the transistor from the case while providing heat transfer at the same time.
