Resetting the PRAM
From Mac Guides
This is a common Mac troubleshooting procedure, and fixes a multitude of software and hardware problems.
'PRAM' stands for 'Parameter RAM', and contains the following stored information:
- Display and video settings such as refresh rate, screen resolution, number of colors
- Time zone setting
- Startup volume choice
- Speaker volume
- Recent kernel panic information, if any
- DVD region setting
Note: Mac OS X stores your preselected DVD region choice in PRAM for easy access. Resetting PRAM does not change the DVD region on the optical drive.
You will not lose any data stored on your Mac's drives, and system and application preferences besides the above will remain intact.
How to Reset your PRAM
- Reboot your Mac
- Hold down Command (Apple) - Option (Alt) - P - R
- When you have heard the chime for the second time, release the keys and the Mac will boot as normal
- Once your operating system has loaded, you may need to verify your time zone, startup volume, and volume settings using System Preferences.
- Macintosh: How to Reset PRAM and NVRAM, Apple knowledge base
- Mac OS X: What's stored in PRAM?, Apple knowledge base