Built-in iSight camera is off?

[MacGregor]

Hey does anyone have experience with iSight cameras that just don't turn on a MacBook Pro? In PhotoBooth I get a dark screen and a camera symbol with a slash through it. It looks like the camera is either broken or disabled. I remember a lot of issues with people wanting to disable the camera, but I never heard whether there is a way of doing it accidently.

Apple website is of course not too helpful since it is assumed that the camera will always just work.

Thanks

MacGregor