Details
For Mac OS X computers, resetting the NVRAM (non-volatile random-access memory) may correct a variety of problems by returning various settings back to the default: display and video settings, time zone, start-up volume choice, speaker volume, and recent kernel panic information, if any.
To reset the NVRAM:
- Turn off the computer.
- Turn the power button back on, then immediately hold down Command-Option-P and R keys simultaneously.
- Continue to hold down these keys as the computer repeatedly restarts. You should let the computer make the normal Mac startup sound 2-4 times before releasing them
This is also a good starting point if someone has a Macintosh computer that won't start and/or has a flashing folder with a question mark.
On older Mac computers, similar information was stored in Parameter RAM (PRAM). Resetting NVRAM on Intel-based Macs using the same key combination is like resetting PRAM.