iSight fails

I have a 20" iMac (2008 model) with OSX 10.6.8. IN the last few days, iSight was not recognized by either PhotoBooth or Skype, but is OK with Yahoo Messenger. I I run Repair permissions with the Disk Utility, it doesn't help. If I run Applejack, it fixes the problem for about a day. After that, it's back to the same thing again. Because it works with Yahoo Messenger, and is fixed temporarily by Applejack, I am suspecting a software problem.

The symptom is Photobooth says "No camera detected" I can attach a USB web cam and that works fine. No something must be moofky-foofky with software, I think.

Any tips will be greatly appreciated as I have some projecvts hanging fire until I get this fixed.