Since upgrading to Mountain Lion my external cinema display is no longer recognised.

Had the same problem with my twin Thunderbolt displays daisy-chained to a new Retina MBP. Very frustrating. Unplugging and replugging the displays worked fine.

I have the same issue when I connceted my 23' cinema display to my 2008 macbook. the display used to work with my laptop in Lion system. but after the upgrade, the display become black. Is there anyone who can help me this? Thanks in advance.

Hey, I have the same problem! I have a late 2008 macbook pro and when I upgrade to mountain lion my external monitor LG (m2294A) sometimes works fine and some other times turns black. Pretty annoying!

I will appreciate any help on this matter. Good day

Hello,

I had a similar problem with my mid 2010 macbook pro (Dell 24 inch external monitor connected with a displayport) that I fixed by resetting the nvram, as mentioned previously, but that wasn't enough apparently. I also had to manually disconect the displayport from the monitor side and reconect it as powercycling forcing detecting screens wasn't giving any results whatsover.

I've done everything in these thread but still no avail...

I was finally able l solve my problem. I bought a 3rd party mini-display-port to DVI cable and switched out the Apple adaptor and it now works flawlessly. Here's the cable I got: http://www.amazon.com/gp/aw/d/B003OBXHPC/ref=mp_s_a_1?qid=1348157137&sr=8-1

How many months must pass before apple addresses this, this has been a known issue since July at least. Every display in my place has issues with this nonsense, and the only real solution has been to downgrade back to Lion. I can only do this with my home machine as my work laptop must remain updated to match the work system. This sort of thing drives me so crazy I can't even begin to voice my anger, why did I pay this company to upgrade my technology when all it did was force my monitors to go dark?

DO SOMETHING APPLE

Hello rbarba23,

I posted my comment on the issue today. Have you had any solutions yet?

https://discussions.apple.com/thread/4803646

Pressing "alt/option" after checking the plugs for tightness worked for me.

Sony Bravia flatscreen via hdmi cable.

While this may be an old thread, apparently the issue still exists as it happened to me yesterday after upgrading from Snow Leopard to Mountain Lion... no external display recognition. I recall having this problem the very first time I attampeted to connect two external displays to a MBP some three years ago using a Diamond adapter. I had to download the Diamond driver in order for it to work. And so yesterday, after all else failed, it all started to come back to me... how, once I learned I needed the driver, & having gone to the Diamond web site where the driver was unavailable, I was directed upon a google search, to displaylink, where one can find a free driver download.

And so I thought, it's worth a shot for it's very possible the upgrade had erased the driver. After downloading the driver, shutting down my computer & unplugging everything, I started the computer back up & reconnected all the hardware & it immediately recognized my two HP displays!