Hey there char4627,
I understand that you are seeing an issue with your ability to record a movie in QuickTime. I have some suggestions for you that may help you address this issue. First, I’d like for you to try to open Photo Booth on your computer, just to make sure that your camera on your computer works as expected:
OS X El Capitan: Apps included with your Mac
https://support.apple.com/kb/PH21852
If that app works as expected, then you may want to try booting your Mac into Safe Mode and testing the QuickTime behavior from there:
OS X El Capitan: Start up in safe mode
https://support.apple.com/kb/PH21875
Take care, and thanks for visiting the Apple Support Communities.