You need a DMM.
Check to make sure you have 12V on your battery & REM inputs, and 0V on the ground. With it still measuring DC voltage put the probes across the output terminals (the ones that go to the speaker) and check for any voltage when you first turn the amplifier on (during that split second before it goes into protect). If it has DC on the output that will cause it to go into protect. You could also check to make sure the outputs aren't shorted by measuring the resistance across the output terminals (DMM set to the resistance, which is the setting with the Omega symbol).
Thats about all I can think of right now. If all that checks out, I'd say there's an internal problem. The amp can be blown and not have any burned parts inside.