MacOS – When the external display is on, the Mac thinks it’s off. When it’s off, on

displaydisplayportmacbook promacos

Hardware details:

Yesterday everything worked fine. Today when I connect the display to my laptop or turn it off or on, I get a blue screen on the laptop for a second, but then it goes back to normal.

The weird thing is that in the System Preferences > Displays preference pane, when the display is plugged in and ON it doesn't detect it, but when it's plugged in and OFF "Gather Windows" appears right beside "Detect Displays, and you can drag windows off the screen where the display should be.

The "Gather Windows" button allows me to see the Displays window for both displays. I've used it to play around with the resolution but this did not work.

Any idea what could be going on?

Best Answer

Restart you Mac and try resetting the PRAM:

Hold down the ⌘+⌥+R+P keys until you hear the start up chime two times.

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