Fix Photo Booth’s Black Screen in Yosemite
There are several reasons this problem could be caused. In my case, running Yosemite 10.10, Photo Booth had a black screen and the menu was saying “no camera connected” although FaceTime worked fine.
The common sudo killall VDCAssistant solution didn’t work at all, as well as, reseting my NVRAM.
After a lot of debugging and trial and error, I found out that the problem originated from the fact that I used Dropbox and had created a symbolic link in the place of the ~/Pictures folder.
The solution is to open ~/Library/Preferences/com.apple.PhotoBooth.plist with Xcode and change the link of ~/Pictures/Photo Booth Library to the absolute path of your new pictures folder.
Cheers~