Caps store up power so the amps have more voltage to use when they need more then you can supply. A car battery wasn't meant for us to be putting huge radio's, subs, 5 amps, neon lights, and all the goodies that we so love to use. A better way to get more stored voltage is to just add a second battery, but sometimes the current isn't high enough...then you need a bigger alternator. Try the cap first though, it's the cheapest route.
Try this....disconnect the amp remote lead from your cd player and connect it(the wire from your amp) to a turn on lead in your fuse box--see if that does anything....
The same thing happened to a buddy of mine. The instructions define all lights that may appear on the amp.
OVER CURRENT - is basically a short in the speaker wires. (It means low impedance across the channels.)
What I need to know:
Are the wires attatched firmly to the subs?
How many subs are you running?
How do you have these wired?
How many channels is your amp? (model # would be great)
Get me this and I should be able to remedy the problem.