Commonwealth Help Desk

Shut down your Mac, then turn it on and immediately press and hold these four keys together: Option, Command, P, and R. You can release the keys after about 20 seconds, during which your Mac might appear to restart.

• On Mac computers that play a startup "chime", you can release the keys after you hear the startup "chime" two times.
• On Mac computers newer than 2016, you can release the keys after the Apple logo appears and disappears two times. 

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