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I use my MacBook Pro extensively in clamshell mode, and when I did this in Lion, the integrated screen would stay off whenever I turned onb the computer because the lid was closed. However, in Mountain Lion, the screen stays on despite the fact that the lid is closed. Is there anyway to force my Mac to detect displays on start up?
Go to Sys Prefs > Displays > (hold Option) and a "Detect Displays" button will appear at the bottom right. The problem for me it's that even though a display is connected and I managed to get the button to show up, it still didn't detected the display until I unplugged and oplugged back again from the thunderbolt port.
I've just upgraded to Mountain Lion on my late 2011 MacBookPro. I've tried hitting the Option key and the Detect Displays button appears. However, no amount of clicking, unplugging, replugging, turning the external display off and on works. Also resetting the PRAM settings doesn't help either.
As I had a few hours headaches yesterday when Parallels was rejected by Mountain Lion, I'm very seriously considering reverting to my previous setup. At the moment I can think of absolutely no benefits in Mountain Lion from my point of view
I'm having the same problem---Mid 2010 MacBook Pro with Mountain Lion recently installed. It would be helpful if Apple would work on this! In the meantime, I'm going to try to uninstall ML.....
Got the detect display button appearing following instructions then... The display that all previous OSXs detected doesnt work.
DOWNGRADING ....... back to Lion or even Snow Leopard it seems.
Mountain Lion doesn't detect displays on startup
