Hello, my name is Dan.
I will do my best to help you, the only stupid question is the unasked one.
Restarting is a good start (sorry) but not enough.
Try a pram reset, this resets the system busses that include the iSight camera.
To do a PRAM reset, you need to restart your machine and hold down these 4 keys.
‘Option’, ‘Command (Cloverleaf or Apple)’, ‘R’ and 'P'.
Keep them down until you hear 4 startup chimes. This is the sound that happens at startup, like a boooonnnngggg.
This resets all of the system buses on your computer, USB, FireWire, display, ethernet and your keyboard/mouse/trackpad.
This will correct many faults but not necessarily yours.
Give that a try and let me know.