Why does secondary screen turns black when selecting “Mirror Display”

display

I have a MacBook Retina.

Whenever I attach a secondary screen, projector or monitor and select the "Mirror Displays" option, the secondary screen turns all black.

It does not matter what connection I use. I've tried the following, and they all have problems:

  • MiniDisplay port to a Cinema Display
  • HDMI to HDTV
  • MiniDisplay -> VGA/DVI converter -> projector

It does not matter what resolution I use.

It all started after connecting it to a projector, where all other presenters using PC was having similar problems.

Best Answer

I solved the problem by resetting NVRAM / PRAM:

  1. Shut down your Mac.
  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 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.
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