I have a problem with my display, at loading time I can't see Apple logo and when I press
option bottom to change the booting device I can not see any thing except a dark screen and my Mac comes out all thing is fine and I have no problem.
This could be related to the PRAM which stores startup disk and monitor depth settings.
Resetting PRAM and NVRAM
Shut down the computer.
Locate the following keys on the keyboard: ⌘, ⌥, P, and R. You will need to hold these keys down simultaneously in step 4.
- Turn on the computer.
- Press and hold the ⌘-⌥-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.