MacBook Pro 15" 2011 display problem at loading 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: &#x2318;, &#x2325;, P, and R. You will need to hold these keys down simultaneously in step 4.
  Turn on the computer.
  Press
  and hold the &#x2318;-&#x2325;-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.