This document explains how to reset the parameter random access memory (PRAM) and nonvolatile RAM (NVRAM) on Macintosh computers.
Important: If your computer does not retain parameter RAM (PRAM) settings when it is turned off, this generally indicates that the battery needs to be changed.
Resetting PRAM and NVRAM
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
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
Your computer's PRAM and the NVRAM are reset to the default values. The clock settings may be reset to a default date on some models.