PRAM (Parameter Random Access Memory) or NVRAM (Non Volatile Random Access Memory) is a chip on the computer that stores certain system information when the power is off. This information is maintained in the chip by a small battery on the computer logic board. Sometimes the system miss-behaves and resetting the PRAM can correct such problems. These types of problems can be manifested in ways such as external ports not working, time incorrect, CD drives not responding and more.

To reset the PRAM do the following:

  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.