librarian7 wrote: ... it works with ... older OS X ...
From your description, your camera should work with 10.11.4.
First, use Apple's http://support.apple.com/kb/HT2090 to check for user-specific problems. You may simply need to change to a user account that does not exhibit the problem.
(BTW - The Troubleshooting article calls the camera an "iSight". However, after the article was published, Apple has changed the built-in camera's name on newer Macs from "iSight" to "FaceTime" and then to "FaceTime HD." Regardless of the name of your built-in camera, the same info and troubleshooting applies.)
To check for user-specific problems, you need to test more than one Apple app (Photo Booth, FaceTime, iMovie, QuickTime Player, etc.) in more than one user account. Do NOT use a "Guest" account for this test. If you have not already established a separate user testing account, create a new one now. If you need help, how to do it is explained in http://support.apple.com/en-us/HT201754.
A "Standard" user account is all you need for testing.
If your cam won't work properly with Apple apps in any OS X 10.11.4 user account, use OS X Recovery to completely reinstall your Mac OS X 10.11.4 from the Recovery System stored on your startup drive. Don't bother testing Skype or other third-party apps until you have your camera working with Apple apps.
Message was edited by: EZ Jim
Mac OSX 10.11.4