How to reset Mac SMC, PRAM, NVRAM

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SMC Reset
  1. Shut down the computer.
  2. Unplug the computer's power cord from both the wall and computer.
  3. Wait 15 seconds.
  4. Attach the computers power cable.
  5. Wait another 5 seconds and press the power button to turn on the computer.

PRAM Reset
  1. Shut down the computer.
  2. Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
  3. Turn on the computer.
  4. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
  5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
  6. Release the keys.

NVRAM Reset
  1. Shut down your Mac.
  2. Locate the following keys on the keyboard: Command (⌘), Option, P, and R. 
  3. Turn on your Mac.
  4. Press and hold the Command-Option-P-R keys immediately after you hear the startup sound.
  5. Hold these keys until the computer restarts and you hear the startup sound for a second time.
  6. Release the keys.
After resetting NVRAM, you may need to reconfigure settings for speaker volume, screen resolution, startup disk selection, and time zone information.