Q: my camera seems to be uninstalled

Reset the SMC, as per > Resetting the System Management Controller

1. Shut down the computer.

2. Unplug the computer's power cord.

3. Wait fifteen seconds.

4. Attach the computer's power cord.

5. Wait five seconds, then press the power button to turn on the computer.

and the NVRAM/PRAM, as per > About NVRAM and PRAM

1. Shut down the computer.

2. Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.

3. Turn on the computer.

4. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.

5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.

6. Release the keys.

Then if it is still not working....? see > How to Troubleshoot iSight

Additionally:

Try quitting all other App's that also use the iSight, because it can only be used by one App at a time.

Go to: Apple > System Preferences > Startup Items and check to see if you have any App set to open at startup that might be getting first dibbs on the iSight camera.

If all of the above fail to get the iSight working, then it may have gone bad and you need to take your iMac in for service.

my isight camera is not working-not recognised with photo booth or ichat

To fix your iSight, shut down computer. Reboot in safe mode (press power button and then hold shift key down). After computer boots, restart again.  Hopefully, your iSight will start working again.