iSight (External) Turns on then off

[-tWv-]

I know this is an outdated piece of hardware, but I need some advice regarding my isight external webcam. Whenever i plug it into my iBook, the green light turns on for a few seconds, then the camera itself makes a sort of grinding noise (like the shutter is closing or something) and then the green light turns off. Does anyone know if this indicates a problem with the camera itself, or maybe it is the firewire cable that has gone bad?

Any help is appreciated, thanks!