Do you have an application like Cheese installed?
When I launch Cheese I get an error “No device found” (which is correct in my environment). What do you get?
Edit: Another thing you can try is:
with the camera switch off, issue the lsusb command
then turn the camera on and reissue the lsusb command
What difference, if any, do you get in the output from lsusb? In other words, does a webcam appear?