My isight has been working fine up until now. When I click on iMovie it brings the screen up but it is black. My green indicator light is off and the camera will not work.

In iLife 09 you import video from the webcam into iMovie 09 under the "File" menu and "Import from camera..."
Dose the webcam work in iChat or in Photo Booth? If it dose you may try reinstalling iMovie.