[Zordrack]

I would start out checking that everything works as assumed.

Get out your volt meter and make sure the amp is getting power.
Both the constant and remote lines.
Make sure ground is good.
Make sure all connectors are properly seated.
Check continuity through the actual speakers.
Check continuity in the line level cables.
Hook up computer speakers to the head unit and make sure it's actually putting out signal.

That's what I would check first.
Never trust the basics. It's always the stuff you assume to be right that end's up biting you in the rear.