Id say get a test speaker and run the amp on very low output, just see if you get a audio signal from the amp, if so then the problem lies in possibly your speaker wiring terminals, very possibly you had everything working for a bit, and one day the speakers may have hit to hard and the internal wire might have come lose. it;s very common problem and a good crimp job on the terminals will often fix many headaches later, check your speakers with the amp and if it works you know your ok. also turn the sterio off and have a freind listen to the speakers, see if theirs any sound at all when the amp is powered up or the headunit is first turned on.good luck with it. love the idea about the 9 volt battery test their kirtec

Take a 9 volt battery and touch the speaker terminals quickly.
they should move and make a noise if they are not blown voice coils.
do not leave the voltage on it for more than 1/2 second,as the dc can burn out the speakers coils