Sometimes your Mac might act strangely for no apparent reason: lights won’t work correctly, volume settings are messed up, the display resolution will change, or maybe your Mac won’t boot at all.  You can solve some problems by closing all your apps and trying to restart the computer. Sometimes, though, you’ll need to reset the SMC, and PRAM or NVRAM.


SMC RESET

  • 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.

PRAM RESET

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