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Asking on behalf of a friend.

His 2011 MacBook Pro (no Thunderbolt) was running Snow Leopard and was being connected to a Dell monitor in the standard way.

He upgraded to Lion and now the MacBook cannot detect the display.

What can we do to detect the display (my Snow Leopard MacBook still detects the display)?

The MacBook was taken into an Apple retail store with the monitor. It was hooked up and obviously didn't work, It was then plugged into my 2006 MacBook, and it worked.

The chap in the shop was very confused.

We then looked at the cables. We used another cable and dvi-mini dvi connector. This changed nothing.

We have also done a fresh install of Lion.

So as for now the problem is unsolved.

As soon as it is fixed I will post the answer.

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    Have you tried a different display or a different cable? You can also go into System Preferences > Displays when the cable is connected and you should see an "Arrangement" tab if it is finding the secondary display. – Nate Bird Nov 14 '11 at 13:52
  • We have not tried a different display, however it works when connected to a macBook running snow Leopard, therfore there is nothing wrong with the cables, or the display. It is not detecting so there is not arrangement tab. – Graeme Hutchison Nov 14 '11 at 14:03
  • If you can try with another monitor then you can for sure know it is the MacBook Pro. You can also give it a restart for good measure. :-) – Nate Bird Nov 14 '11 at 15:01
  • The monitor works. It has been used with a PC as well. – Graeme Hutchison Nov 14 '11 at 15:35
  • Do you mean 2010 Macbook Pro? Because all "2011" MBP's have thunderbolt – abc905 Nov 23 '11 at 1:47
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This is from my own experience, I have macbook pro with lion and a dell monitor, I connect via mini displayport to VGA connector, if I connect displayport first to my macbook and then monitor's vga to displayport to VGA, it won't work, I don't know why but maybe some internal implementation detail, just go in this order

  1. switch on both devices
  2. connect monitor's VGA cable to your mini displayport cable,
  3. connect mini mini displayport to you macbook.
  4. wait for a few seconds, it works every time.
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  • Do you have to do this every time you restart? – Graeme Hutchison Nov 23 '11 at 7:54
  • yes, but I rarely restart and only when OS tells me to do so, also when putting macbook to sleep just remove minidisplayport from macbook(you can leave VGA connected to displayport), and then when you wakeup from sleep just reattach it. – Vaibhav Mishra Nov 23 '11 at 8:46
  • Not really a solution, im afraid, the reason a macBook is used is beacuse its portable, so will be disconnected, otherwise a Mac Mini would have been bought, and this wouldn't be a problem. Thanks for your comment tho. – Graeme Hutchison Nov 23 '11 at 9:12
  • it's a workaround till apple fix this with update however 2-3 days ago they released a thunderbolt update , check if problem is fixed after downloading update. it is definitely a bug. – Vaibhav Mishra Nov 23 '11 at 9:18
  • Its not thunderbolt. – Graeme Hutchison Nov 23 '11 at 10:39
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Mine did this because I had Air Display installed (yes, Air Display). I uninstalled that app and everything works now.

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  • I was annoyed by the fact the external display wasn't being detected automatically for several weeks! It didn't occur to me it was related to Air Display kind of apps. I didn't have Air Display, but I had DisplayPad installed, which was pretty much the same. Merely quitting it fixed the issue! Now the display is being always automatically detected instantly the moment I plug it in. Yay! Thank you so much, sir! – eploko May 24 '12 at 8:43
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Shut down the MacBook. Start it up with the external monitor connected. It should recognise it. Had same problem on Mountain Lion with a projector I had used many times before. Was supposed to be showing a film to a bunch of kids in the Youth Club and had to give up. My wife discovered the next day that restarting with it connected fixed it.

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  • I had the same problem. I saw your comment and I tried it. It works! Thanks a lot! – Evariste Jun 13 '13 at 5:01
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Try a SMC reset first - you might also want to test starting in Safe Boot mode and/or creating a new admin user and logging into that account.

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  • I have tried new users and also safe boot. I will try resetting the SMC and see what happens. – Graeme Hutchison Nov 16 '11 at 14:01
  • This didn't work, he is going to go to the Apple store soon. I will update with the answer. – Graeme Hutchison Nov 17 '11 at 15:28
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I had a problem where my mac was only detecting one of my 2 external monitors after I updated to mountain lion. It just plain was not detecting it. I thought it was only detecting the one that was connected via mini display. Turns our I was using something called Display Link. I don't remember if I downloaded that or if something else did when I first set up my monitors. I noticed that in that file it only had the uninstall in the file. So i went to the website and reinstalled the Display link and that worked! Hope that helps someone!!

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