OR...you can use a multi meter.....you should get 12 volts (or there abouts) with the car and system off at the amp itself. If you dont, then somethign witin the power cable is wrong. Jsut because a fuse is not visually blown, they sometimes will not pass current...especially if you have the AGU glass type fuse.

If you have access to a meter, you can test it pretty easily.