Q: my macbook pro does not detect external display anymore

I had this issue with a Samsung monitor and my MBP - BUT I haven't had a single  problem since I changed my apple minidisplayport adaptor (then connected to a DVI>HDMI cable) to a generic cable from Amazon that is direct minidisplay port connector to HDMI.  I think the Apple minidisplayport>DVI adaptor is perhaps overly fussy in its negotiations with the monitor.

Well, it happened again today and now nothing works. Guess I can put the montior in the closet.

Went to the Appe genius yesterday to get a diagnostic on my MBP. It needed a new battery (5 years is a long time for a battery), plus discovered that ML was not completely downloaded, even though all surface info told me it was.

Redowned loaded and installed ML, and now the external display and MBP communicate very well.

this is the thing that finally did it for me! thanks so much! Panasonic Viera 42" monitor working wonders now with my MBP! I had tried literally everything else

Heya guys I see this started a long time ago I had all the same issues

Tried every thing even talked to an apple tec that went through reboots

And heaps of trouble shooting steeps for two hrs to no avail

Thanks for trying brad in au . I bit the bullett and took my Mbp into

Harvey Norman in New Zealand got one of there guys to put in a

Mini display to hdmi brand moshi connect and  Wamo it worked  ASAP.

$60 bucks ouch but saving on the disprin aspirin panadol Wea Eva ur from

From the hrs spent messing around with it . Lesson learned don't buy cheep .

My Mbp is mid 2012 thunderbolt port the cable at the hdmi end is a bulk looking

Box I'm guessing that apple put a software patch on mini display as it doesn't just

Look like a plain cable any more . Hope this helps

you  just saved my day. thanks!

I have a new MacBook Pro, new Dell monitor and new Apple mini dvi display adapter.  Suddenly my Dell monitor was never detected again.  I tried each suggestion posted here but to no avail.  However, this worked for me:

With mbp running; disconnect mini display adapter

Detect monitors (option + command + F2)

Reconnect mini display adapter

(now both monitors work)

I only needed to do this once, so I cannot be too certain if it will work again. 

Thanks so much - this fixed our problem. 2012 macbook pro 17" with cinema display on mountain lion.

Same issue started today.  24" ViewSonic has been working flawlessly for a year.  I always use it with my 2011 MBP 13" lid closed.  So I wake up the computer with the wireless trackpad or keyboard.  NEVER once had an issue.  Then this morning the ViewSonic would not respond.

I opened the MBP, checked the displays and it showed that it recognized the ViewSonic even though the ViewSonic screen was black.  I did all sorts of different reboots and disconnect/reconnects with both the MBP and ViewSonic but the best I could muster was a mirror image on the ViewSonic only when the MBP lid was open.  But the Viewsonic image was distorted (resolution was screwed up).  Considering I use the Apple Mini-port HDMI adaptor, the ViewSonic picture was always crystal clear before today. 

No matter how many times I opened and closed the lid and then tried tapping on the wireless trackpad, it never woke the computer.  Until I did this, and it's been working all day and night since doing so:

1.  Make sure the monitor and MBP are connected, and the computer is running and lid is OPEN

2.  Disconnect the Apple Mini-port adaptor from the MBP

3.  Unplug the power source to the ViewSonic (or whatever external monitor you're using).  Wait for the standby light on the external monitor to go off before taking the next step

4.  Reconnect the Apple Mini-port adaptor to the MBP (HDMI or DVI cable should already be connected the Apple adaptor - I'm assuming this throughout these steps)

5.  Reconnect the power source to the external monitor

Give it a few seconds and the display should now show up on external monitor.  It will likely be distorted which we will fix in the next series of steps.  Make sure you have checked mirror displays in the display preferences.

Now, to get the MBP to recognize the external monitor when the lid is closed, do the following:

1.  Make sure the the MBP lid is open and the computer is on.

2.  The display on the external monitor should still be mirroring what you see on the MBP screen (although the display will be distorted).  Now close the MBP lid (do not put it in sleep mode, just close the computer while it's running.

3.  Now unplug the Apple Mini-port from the MBP.

4.  Unplug the power source to the external monitor.  Wait for the stand-by light to go off before going to the next step

5.  Connect the Apple Mini-port back into the MBP

6.  Reconnect the power source to the external monitor.  Immediately start repeatedly clicking the wireless trackpad or mouse until the display stays on.  It will blue screen for a sec while it resolves the resolution.  It should then come back on and look as it should.  External monitor should now be ready to use with the MBP closed

What does ML stanfd for?

ML = Mountain Lion (Apple OS X) I think.

Have just received my MBP back from the Apple Shop after suffering this problem a couple of weeks ago. Apple had to replace the entire logic board - thankfully it was under the Applecare warranty or I'd have been shelling out around £400.

I have a feeling the miniDV link was the problem - probably the connector blew and took out some components with it though the rest of the Mac (apart from throwing a signal to the external screen) worked fine. Now it's all working fine - phew!

OK guys, my problem was resolved. In my case problem was the original adapter thah was broken I bought brand new and began to work. It's very strange why the adapter is broken.

Catherine, thank you so much for the trick. I Have a macbook air conetcted to a HPx2301 and had the same problem for a couple of days. I did what you sugested and voilá!!!

looks like the new update is what causing the problems i havent had this issue but i am not the updating type either i suggest you find i way to downgrade your mac.ope it helps

I encountered this issue intermittently since purchasing my MacBook Pro and ViewSonic monitor in December.

Because I had nearly every port filled (mic, monitor, backup drive, iPhone), to free up slots and make it easier to disconnect at night I picked up the new Belkin Thunderbolt Express Dock. Everything plugs into that and it connects to the MacBook Pro with via one Thunderbolt cable. Very clean.

A pleasant surprise bonus: The ViewSonic now connects the way it should - and I haven't had the issue since. I'm not sure exactly how in technical terms, but the dock bridges the gap between the MacBook Pro and the ViewSonic, making the monitor Mac-friendly. Anyway, it just works.