Troubleshooting a Mac – Boot Options
Every once in a while a Mac gets so messed up that it won’t even boot. It’ll sit at the Apple screen, turning away. Or it’ll kernal panic just as it hits the blue login screen.
From Apple’s Support Knowledge Base here is what you need to do.
Resetting PRAM and NVRAM
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.
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.
If you have an older PPC Model Mac such as a G5 or Powerbook there is an additional step which will help.
Boot into Open Firmware by holding down the ‘Command-Option-O-F’ keys from a cold start while the chime is being played. You will see a command-line screen…enter these commands:
1. At the Open Firmware prompt, type: reset-nvram
2. Press Return.
3. At the Open Firmware prompt, type: reset-all
4. Press Return.
Example:
0 > reset-nvram
Press Return
0 > reset-all
Press Return
The reset-all command should cause the computer to restart. If this occurs, you have successfully reset the Open Firmware settings.