Apple support article:
More information here:
If you monitor the "More Like This" box (top right), other threads appear. Opening them usually displays other threads.
When a setting such as monitor resolution changes without reason, suspect the PRAM. Try a PRAM reset:
Copied from Apple Knowledge Base: http://support.apple.com/kb/ht1379
- Shut down your Mac.
- Locate the following keys on the keyboard: Command (⌘), Option, P, and R. You will need to hold these keys down simultaneously in step 4.
- Turn on the computer.
- Press and hold the Command-Option-P-R keys 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.
After resetting NVRAM or PRAM, you may need to reconfigure your settings for speaker volume, screen resolution, startup disk selection, and time zone information.