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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?

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Have you tried anything to get things working yet? If so, what? –  Robin Feb 14 '12 at 20:54
    
I tried resetting the PRAM as suggested below. I'm also going to get a Apple brand Mini DisplayPort to HDMI adapter, which seemed to help in the case of: apple.stackexchange.com/questions/5174/… which seems like a similar problem. EDIT: actually he just bought another adapter, not an apple one, and it might have been a firmware update that actually fixed it. –  seagreen Feb 14 '12 at 21:02
    
Have you done the MacBook Air EFI Firmware Update 2.3? –  MrDaniel Feb 15 '12 at 19:30
    
I don't see EFI Firmware Update 2.3 in Installed Software, but when when I tried to install it I got a "This software is not supported on your system" alert. Would it be appropriate to start a new question to get help with that problem? –  seagreen Feb 18 '12 at 6:56
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3 Answers

Problem solved. It was a bad HDMI cord. I had tested it on a friend's computer and it worked, but I hadn't tested other HDMI cords on my computer until this evening. I've now tested a new HDMI cord with three adapters and it works on all of them. The old cord works with none of them.

Sorry to trouble you all for such a simple problem. If anyone has an explanation for weird interaction described in the title of the original post I'd still be curious to hear it.

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You can also try to reset the 'System Management Controller (SMC)' as described here: http://support.apple.com/kb/HT3964

Take note of the following description:

"After performing normal troubleshooting, these symptoms may indicate that an SMC reset may be necessary: [...]

Video

A computer that supports target display mode does not switch into or out of target display mode as expected.

A computer that supports target display mode switches into or out of target display mode at unexpected times."

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It's still doing the exact same thing, unfortunately. Thanks for the suggestion. –  seagreen Feb 18 '12 at 7:23
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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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Thanks for the suggestion, but unfortunately everything's still the same. –  seagreen Feb 14 '12 at 21:01
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