Here's a really simple test;
Tap on the sub with your fingers.
Does it move freely like it should? Or does it have a little resistance and make scratchy sounds? Or worse, does it not move at all? If it's moving free, but you're getting no sound out of it at all, I'm afraid to say you may have burnt the VC.
Have access to a multimeter? See if you've got continuity across the sub terminals, and what the resistance is if you do. Move the sub with your hand while you have the multimeter set for voltage across the terminals and see if you get anything.
HTH
