My iMac Intel (2010) no turn off.
iMac, Mac OS X (10.7)
Press and Hold the Power button until it shuts off. Then I would recommend you Reset the SMC and the PRAM:
Resetting the System Management Controller (SMC)
- Shut down the computer.
- Unplug the computer's power cord.
- Wait fifteen seconds.
- Attach the computer's power cord.
- Wait five seconds, then press the power button to turn on the computer.
- Shut down your Mac.
- Locate the following keys on the keyboard: Command (⌘), Option, P, and R. You will need to hold these keys down simultaneously in step 4.
- Turn on the computer.
- Press and hold the Command-Option-P-R keys before the gray screen appears.
- Hold the keys down until the computer restarts and you hear the startup sound for the second time.
- Release the keys.
Hope this helps