If you have another speaker you can hook up to test the wires, try that. I brought out one of my small home stereo speakers to make sure it was the speakers, and not the wires. If the speaker works, go buy a new pair of speakers. My rear speakers didn't work in my truck when I got it. 1: The PO didn't even have the rear speakers wired up and 2: The speakers were blown.
If it doesn't work, pull out the unit and make sure the speakers are wired up right.