IMac external display not recognised although previously it was recognised.

I have been using a secondary display for several months without problems. Now the iMac refuses to recognize it's existence. The secondary display gives message 'No Input Signal' Any ideas as to what has gone wrong?

No other settings that I know of on the monitor. What is puzzling is that it has worked for three months and I have not knowingly changed anything apart from OS updates. The iMac just does not detect the second monitor so it is not appearing in Display Settings dialog.

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I have a Samsung Syncmaster 2443BW which I wanted to set up as extended display for my new bought Macbook Air.
I am running the latest Mountain Lion OS including the last updates.
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Any help is appreciated - thanks!

If the system is from Dec. 2011 it either came with DVD discs to reinstall the original shipping version of OS X or it came with Lion preinstalled.
If Lion then you use the Online Internet Recovery system to reinstall Lion, No Password needed. To boot to the Online system at startup hold downn the Option/Alt + Command + r keys and hold them down until you see a globe on the screen. From the Mac OS X Utilities screen that comes up use Disk Utility to partition the drive as one partition, Formatted Mac OS X Extended (Journaled) with a Partition table of GUID (That is an option under the Options button). Then click the Apply button. Once that is done exit DU and select Reinstall Mac OS X.
If it came with system Reinstall discs you have to use those to reinstall OS X and the iLife apps then you can use the Mac App Store to upgrade to Lion, Mt Lion or Mavericks. Whichever version you bought from the App store perviously or Mavericks for free.

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I have an iMac 3.4 Intel Core i7, have used an external monitor for a program for ever. Upgraded to Mountian Lion and no more external monitor.

Update/Fixed - I talked with Apple support via phone since I had 90 days of complimentary support. After describing my troubleshooting the rep recommended reinstalling 10.9. I did that this morning and the remote monitor is back in service. So it appears something broke in 10.9 that is fixed by the re-install. It would be nice to know if it's a simple preference that could be trashed. But it looks like hardware is not the issue.

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I assume you mean System Information?
The Thunderbolt Bus information reads:
Firmware Version: 23.4
Port:
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     Link Status: 0x7
     Link Controller Firmware Version: 0.12.3
Port:
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20" Apple Cinema Display not recognised after upgrading to OS 10.8.2 (Mountain Lion).
Hello Apple! Anybody there? How long does your community have to wait for a solution?
The same problem has been unsolved for months now. No statements from Apple either.
I was told today to wait for 10.8.3. This might solve the issue. I can not belive my ears.
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I found out that I needed a $100 mini displayport to dual-link dvi adapter to make my $30" cinema display work with my macbook pro
http://store.apple.com/us/product/MB571Z/A/mini-displayport-to-dual-link-dvi-ada pter?fnode=51
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Macbook (Late 2007) External Display Not Working

I have an acer x243hq 1920x1080 external monitor which works with my Xbox 360 (vga cable) and my friends macbook (early 2008) but not my macbook
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i have all current updates
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Have you downloaded the Mac OS X (10.5.4) Combo Update? I posted my problem, very similar to yours, and in researching it I found it at: http://www.apple.com/downloads/macosx/apple/macosx_updates/macosx1054comboupdate .html. It might just be what you need!
My problem is that I am running 10.5.7, which I blame for my external display not acting like it did when I was on 10.5.6! One expert at Apple Support told me to erase my HDD, reinstall Tiger, upgrade to Leopard again, but only to 10.5.6! Has anyone any idea as to when 10.5.8 is due out? Is there a Beta?

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I have a 27" iMac (newest model) and have been using it with a BenQ BL2710 monitor. It's connected with a mini display port to display port cable. It's been working great; I found that I had to uncheck the 'Displays have separate spaces' box in Mission Control, so I have the menu bar on the iMac'd display only.
Now, I have a 2nd BenQ BL2710 that I'm trying to hook up the same way, using the iMac's 2nd thunderbolt port. The display powers up and all 3 screens look perfect. The problem is getting the arrangement correct. I have the dock on one display, the menu bar on another, and the mouse will only work on one or two of the displays, depending on how I change the arrangement.
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I just answered my own question; apparently with two external displays connected, the dock has to be positioned on the bottom. I had it on the right of the main iMac display. Moving it to the bottom, and rearranging the position of the monitors in display preferences did the trick.
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Seagate external hardrive not recognised by Imac after wakeup / start up

Hello,
I use this seagate external 1tb driver / mac version silver/ for the time machine
and almost every time I startup my Imac seagate will not start with it or show in finder, unless
I unplug the firewire and plug it back again.
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I would appreciate if someone could help me with how to fix that.
Many thx in advance
and Merry Christmas to you all

Is this the type of enclosure that power on and off automatically, based on the state of the Mac (no need to flip a switch)?
Does it also have a USB connection on it? If so, if you connect by USB 2.0, does it have this same problem?
Did it work properly before and recently stopped working, or did it aways have this problem?

Laptop Built In Display and External Display not Working

Hi all, I have a HP Envy M6-1158ca, and recently my Built-in display stopped working. I plugged it into an external display via HDMI and it showed no input. It seems as though the laptop is not booting into Windows either, as usually whenever my laptop boots into windows, the fingerprint scanner blinks letting me know I can now sign in using it. I am extremly frustrated with this, and have an unbelieveable amount of stress because this was my only PC. Please respond as soon as possible, it would be much appreciated.
Thanks in advance.
This question was solved.
View Solution.

Yes.. i think thats what might have damaged it...Notebook should always be completely powered off with the battery out and ac adapter disconnected while replacing any internal hardware..
Shouldnt be a BIOS problem....but still you can check this link..
Restoring the BIOS
Note:
If you have HP Support Assistant installed on the computer(The Blue Question Mark) then open it ==> Complete all pending Updates & Tuneups==> Restart and Check. It may solve your problem
Although I am an HP employee, I am speaking for myself and not for HP.
**Click on “Kudos” Star if you think this reply helped** Or Mark it as "Solved" if issue got fixed.

External Display not working (descriptive details in post)

Hello
Background:
I have been using a black Macbook (last year's model - before the aluminum ones came out) and connecting it to a VIZIO VW22L HDTV10T (television/monitor) via a mini-DVI to VGA adapter.
This setup always worked, although it was a bit finicky (I'd have to plug it in before closing the display to get in to work in clamshell mode, for example). I get the feeling from reading other forum posts that this is the normal case, though (which so far has been my only real gripe with OS X).
Anyway, back a couple months ago I wondered if this finicky-ness was partially caused by a messed-up preference file, so I decided to try and fix this. In the ensuing tweaking, I somehow caused my Display preferences to disappear.
After much effort trying to fix the problem, I eventually called Apple support, which ultimately recommended that I reinstall OS X. I didn't do that, and continued to work at the problem. I eventually was able to bring it back by going into my Time Machine backups and restoring all the Display preference files (I used old preferences from back when I got the external HD, so I knew they'd be "uncorrupted). However, now I'm having problems with my external display, namely that it is not working.
This problem started early this year, so it might have been caused by the 10.5.5 update, but since I had all these other problems going on, I'm not sure if that was the case.
Problem:
The Macbook doesn't seem to recognize the display, or is having problems routing video to the display, or something.
If I plug the display into the Macbook while it is running normally, the Macbook LCD will flash blue (like it picked up a new display), but them come back to normal. The monitor will go out of sleep mode for a second, but then display a "No signal" message. If I attempt to "Detect Displays" the Macbook screen will either flash blue (as before) or just do nothing.
If I have the display plugged in when I start up the Macbook, everything will proceed as normal until the time the desktop would be displayed. Instead of this, I just see a blue screen (like some generic desktop before any background is applied). The menu bar, the dock, and icons do not show up. However, I can hear various audio cues telling me the computer is running fine except for htis problem (email notifier going off, etc.).
I know the problem is not faulty hardware, because when I boot my Macbook into Windows, everything works perfectly. It therefore follows that it is an OS X problem. I downloaded both Cocktail and Applejack and run various repairs on them (most notable repairing preferences), but nothing has changed.
Any suggestions about how to try fixing this? If there's any technical detail I've missed, let me know.
Thank you in advance to everyone who tries to help.
-Richard

I have same problem. MacBook Pro (new, 2014) upgraded to Yosemite. Had been running with ViewPoint high-resolution, 27" monitor, HDMI. I tried Thunderbolt connection -- it connected, but it would not allow the external monitor to run at its native resolution (2560x1440). It would only display properly using HDMI. Just 3 days ago after I installed the latest OSx software update, and my external monitor problems started. On startup, my MacBook screen flickers non-stop. I can fix problem eventually (after several tries) by disconnecting the HDMI cable, turning OFF the external monitor power, turning external monitor back ON and then plugging in the HDMI to my MacBook Pro. This is very inconvenient.
I will try using the Thunderbolt cable. When I tried it in the past, it connected, but it wouldn't display the native resolution of my external monitor (which is 2560x1440). Can only get this resolution now with HDMI.

Imac - external display stopped working

Hi All,
My imac has developed a problem overnight. I usually have the imac connected to an external display via the mini-DVI connection and everything worked fine. (to DVI --> HDMI --> Pioneer Plasma).
However today the imac could not be awoken from sleep. Restarting gets to the desktop screen but then goes gray screen. After much troubleshooting, I have isolated the problem to the mini DVI port. The computer will not complete booting up if the mini dvi port is connected. Just in case it was a problem with the mini-dvi to dvi adaptor, I tested it with a mini dvi to vga adaptor. Exactly the same problem with the booting sequence (gray screen as it gets to the desktop image stage). Without the mini DVI port in use, the imac boots up fine.
Could somebody please give me some suggestions re any further troubleshooting procedures I could try to fix the problem, or does it sound like a videocard hardware problem? Thanks for any thoughts.

Welcome to Apple Support Communities
Try doing a Parameter RAM reset - hold down command/option/p/r keys at start up and wait for three chimes before releasing the keys.

New 27inch iMac, external Display "blinks" while in "Display Sleep"

I just updated from a 24inch iMac to a 27inch iMac.
I'm using the same setup for connecting the external display, which is a miniDisplay Port adapter(from Apple) to DVI, then DVI to the external monitor.
All works fine until the "Sleep Display" kicks in, then the external monitor pops up the "DVI-I no signal" warning. This is normal but instead of going away after a couple of seconds it begins to blink as if their is communications going on between the monitor and iMac. So its blinking this message endlessly and thus the external monitor never really goes to sleep.
Since this worked fine on the iMac 24inch, I'm assuming it has something to do with the "Thunderbolt" port, using a miniDisplay port adapter.
The external monitor is a 20 inch Viewsonic VP2030b, running at 1600x1200.
I added a YouTube video for clarity. http://www.youtube.com/watch?v=Q7Zm_U_7sbc

Go to: System Preferences > Displays select the Color tab > uncheck "Show profiles for this display only" and try one of the RGB profiles to see if it is better for you.
Then if you are not happy with one of those..? Try Selecting, Calibrating and Saving a different Profile, other than the default one offered for that monitor.

IMac & External Display & Aperture - Experiences

I have been thinking of getting the new quad core iMac to use with an external monitor for photo editing, relegating the iMac built in display to doing what it does best - acting as a looking glass!
From my own experience and reviews I have read on the web, the performance of Aperture is significantly affected by the graphics card. So what I want to ask is, has anyone here tried this and if so what effect on Aperture's performance does connecting an external display have? If it has an effect do you still find Aperture 'fast enough'? Yes I know 'fast enough' is a relative term and what one person deems fast another may find slow.
Thanks in advance any answers appreciated.
P.S. Is there any way to switch the iMacs built in display off and just use the external display?
John

Hi John
You can not turn off the iMac display, but it shouldn't be a problem if you run the setup in Extended Desktop Mode and then use the connected display as your main Display. Go to: System Preferences > Display's > select the Arrangement tab, then turn Mirroring Off and drag the menu bar to the connected display.
The display on the right is my 17" iMac Display, but I use my 21.5" LG on the left as the main Display. I run most of my Applications on the 21.5" LG Display and use the 17" iMac Display for Finder, iTunes, Tools, Preference panels and other Utilities.
Dennis

IMac external display problem

Hi,
I have a spare 22" 1080p tv sitting around so I tried to set it up as an external display for my 21.5" iMac. I was able to get it working (MDP to HDMI) but the resolution and color is not so great, and when I look at the external display in System Profiler it says something about it being a tv (which it is). My question is can I do anything better than what I have experienced so far? Thanks for the help,
rc
Note - I also tried running the Color Profile app that appears on the external display and while it did improve it some once I clicked on save it never seemed to stick...

Go to: System Preferences > Displays select the Color tab > uncheck "Show profiles for this display only" and try one of the RGB profiles to see if it is better for you.
Then if you are not happy with one of those..? Try Selecting, Calibrating and Saving a different Profile, other than the default one offered for that monitor.

24" iMac - external display limitations

1. I have a mid-2007 24" iMac. I believe this means it has a ATI Radeon HD 2600 PRO with 256MB of GDDR3 memory. The ATI specs suggest that this might be capable of driving a separate external display of 1920x1200 or maybe up to 2640x1600. I'm considering a Dell U2711 or maybe a 27" ACD -- these have a native resolution of 2640x1440. So will my old iMac do the job?
2. What options do I have to drive two external (independent) displays on this iMac? An inexpensive way to gain a lot of screen space is with a pair of external 24" displays, each at 1920x1200. Run one off DVI directly from the iMac and a second on a USB display adapter? Or... ?
Thanks for any feedback.

I see, I'm guessing you need the additional resolution otherwise you wouldn't be asking? If so then you're probably going to have to upgrade to a new iMac. Considering your computer is 3 1/2 years old I'll bet you've been dying for a new iMac. Assuming yours is in good shape you could sell it and then upgrade. I'm not sure what they 're selling for these days but you could check Ebay or your local Craig's List to get an idea. Just a thought.....

IMac external display not recognised although previously it was recognised.

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