Q: Please! Camera does not work on my Mac

How to Troubleshoot iSight

(Over time, 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 Mac's built-in camera, the same info and troubleshooting applies.)

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OS X Mavericks: Reinstall OS X