This applies to MacBook Pro models introduced in mid-2009 through 2017, MacBook Air models introduced in 2017 or earlier, and all MacBook models except the MacBook (13-inch, Mid 2009).

Shut down your Mac. On your built-in keyboard, press and hold all of these keys: Shift on the left side of your keyboard

on the left side of your keyboard Control on the left side of your keyboard

on the left side of your keyboard Option (Alt) on the left side of your keyboard While holding all three keys, press and hold the power button as well.

Keep holding all four keys for 10 seconds. Release all keys, then press the power button to turn on your Mac.