Power or other problems related to unexpected system sleep, shutdown, lights or fans call for an SMC reset:
Resetting the SMC on Mac portables with a battery you can remove
- Shut down the computer.
- Disconnect the MagSafe power adapter from the computer, if it's connected.
- Remove the battery (to remove the battery - click here: MacBook or MacBook Pro).
- Press and hold the power button for 5 seconds.
- Release the power button.
- Reconnect the battery and MagSafe power adapter.
- Press the power button to turn on the computer.
Still having problems? Replace steps 6 and 7 with the following:
6. Reconnect MagSafe power adapter.
7. Press the power button to turn on the computer,
8. Then reconnect the battery.
Resetting the SMC on portables with a battery you should not remove on your own
- Shut down the computer.
- Plug in the MagSafe power adapter to a power source, connecting it to the Mac if its not already connected.
- On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time.
- Release all the keys and the power button at the same time.
- Press the power button to turn on the computer.
Resetting the SMC for Mac Pro, Intel-based iMac, Intel-based Mac mini, or Intel-based Xserve
- 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.