Currently Being ModeratedJun 12, 2013 4:20 AM (in response to SheelaghE)
Make sure that FaceTime camera is listed.
Click in the menu bar.
About This Mac > More Info.. > System Report > Hardware > USB > FaceTime HD CameraBuilt-in)
Make sure that time and date are set correctly.
If the suggestions made in these articles do not help, contact Apple.