• If you have not already done so, restart Mac and
try again. If the iSight still does not work, continue.
• If Apple's http://support.apple.com/kb/HT2090
suggestions do not help you, (are you certain that you
used the correct "reset" procedure?), yours is most likely a
hardware problem that will require a professional fix.
Unless you have a current backup, make one now.
Then use the final "Troubleshooting" suggestion:
"... contact Apple or an Apple-Authorized Service Provider for service."
• If you want to try one more thing on your own first,
use Disk Utility to repair permissions. Then
download and apply the latest Combo Update for
your OS: http://support.apple.com/kb/DL1582
• Repair permissions again immediately following the system restart
that completes the Combo update.
Properly applying the Combo version of updates can sometimes correct software problems, but, if your trouble is caused by a hardware problem, there are no user serviceable parts of iSight.
(For other readers: 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.)