Could be a hardware issue. The webcam stopped on my mini9 a while ago. I booted up Ubuntu and it didn't work with that either, so I guessed it wasn't an OSX issue.
Looked around the forums a bit and apparently there can be a lot of tension on the cable from the webcam to the motherboard (through the hinge on the screen) and that can pull out the connection for the webcam.
Haven't had a chance to take my dell apart and try to fix it yet.
Of course, your issue may be nothing like that. But you could try asking in the general (non-OSX) part of the forum to see if anyone can give you any pointers on how to tell if it's a hardware issue.