If your FaceTime HD camera isn’t working…
I’ve been there. Got a brand-spanking new MacBook Air 11" last year to double my memory and disk space, and loved it! Lo and behold, my FaceTime HD wouldn’t work on any non-Apple applications, including Google Hangouts inside of Chrome. After a fair bit of Googling, I found a terminal command that temporarily fixes the problem:
sudo killall AppleCameraAssistant
While this is only a workaround, at least I was able to use Hangouts. Hope this helps someone else. Got to pass it along!