Options for solving this issue vary and many users report varied success as well. First steps include opening Disk Utility (Applications > Utilities) and running a Permissions Verify and Repair. Once completed, reboot your Mac and test your iSight camera. Another place to check right away is if you are using, or have used, Skype. Skype tends to maintain control of the iSight camera in its preference file which can cause other applications that are attempting to access the camera to not see it (even if Skype is closed). To solve this, find the Skype preference file (com.skype.skype.plist), located in (username > Library > Preferences) and drag it to your Desktop. Try out your iSight in iChat and if it works, delete the Skype preference file.
Users may also attempt resetting their PRAM and/or SMC:
- Shut down your Mac.
- Press the power button to start your Mac, holding (Command + Option + P + R) until you hear three tones.
- Shut down your Mac.
- Disconnect the AC power and remove the battery. For newer Mac notebooks with non-removable batteries, keep the AC power source plugged in, press the (Command + Shift + Option) keys, and press the power button once. Wait about five seconds and press the power button to start your Mac.
- In older Mac notebooks, once the battery is removed, press and hold the power button for about five seconds and release.
- Reinstall the battery and connect the AC power. Press the power button to start your Mac.
Alternative places to check
Apple Support Discussions user "Ralph Johns" reports:
In Leopard there was an App called iSight Update app that was in Hard Drive/System/Library/Core ServicesIf the camera is indeed in use by a Web browser, be sure to reset Safari (from the Safari menu bar > Reset Safari...), Firefox, or whatever browser you use. Users can also reference this Apple knowledge base article about troubleshooting their external iSight.
This does not seem to be there in Snow Leopard.
An issue with some computers with the camera was that in System Preferences > Displays the Colours needed to be set to Millions.
Also check the Hard Drive/System/Library/Extensions folder and see that you have the Apple_iSight.kext (this is likely to handle the Internal iSights as well).
One last thing.
Some Web sites can make use of the camera using Flash.
If that tab is still open the Browser may have use of the camera.
It sounds like you have done computer restarts and this will not be the case unless the browser is set to go back to that page.