This video will show you how to Reset the SMC System Management Controller on a Macbook Pro Macbook and Macbook Air.
Apple have said
Note: It is possible that the SMC could encounter an issue that may cause unusual system behavior typically related to the symptoms described below. In some cases, resetting the SMC may be the only correct method to resolve the issue, however, an SMC reset should only be attempted after all other standard troubleshooting has been performed.
You should try the following steps before you reset the SMC on your Mac and test the issue after each troubleshooting step and see if the issue still occurs.
Step 1. Press the Command, Option and Escape to quit any application that might not be working properly.
Step 2. Put the Mac in sleep mode by selecting the Apple menu button in the upper-left menu bar and choose Sleep. Wake the Mac after it goes to sleep.
Step 3. Restart the Mac by going into the Apple menu and choose Shut Down.
Step 4. Shut down the computer by going into the Apple Menu and choose Shut Down.
Sometimes your Mac might appear to be running normally but it doesn’t seem to be responding, you can force the Mac to shut down by pressing and holding the power button for 10 seconds.
NOTE: Any unsaved work will be lost.