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Dual monitor not working

Posted on 2016-11-10
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Last Modified: 2016-11-14
I have two computers which have two screens one 20” one a 32”

I can’t have to computer display on both screens at the same time, the computer will only displays on one at a time
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Question by:Abraham Deutsch
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19 Comments
 
LVL 21

Expert Comment

by:CompProbSolv
ID: 41882723
When you say "one at a time", how are you switching between them?

Try the following:
Right-click on the desktop
Left-click on Screen Resolutiom

How many monitors do you see in the upper box (to the left of Detect and Identify)?
If there are two, then click on each and select "extend display" in the lower drop-down box (once for each display).
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LVL 88

Expert Comment

by:rindi
ID: 41882750
How are the displays connected to the PC? Does your video adapter support multiple displays? Have you installed the proper video adapter drivers for your OS?
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LVL 2

Author Comment

by:Abraham Deutsch
ID: 41882828
When both are plugged in at the time of starting the computer it will show two, but only the 20” will work and when pressing Identify nothing will show on the 32” (the 32” will be grayed out). If I start the computer with the 32” plugged in the computer will stared on the 32” and then (after starting up the computer) it will only show one screen.

I updated the drivers and even tried a new video card.

On the other PC I have two 20” monitor working fine, but cannot add the 32” via a converter to USB, and even when removing the second 20” monitor and plugging in the 32” directly to a display port (not convert to USB) it does not work (It worked for a few hours then it stopped)
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LVL 88

Expert Comment

by:rindi
ID: 41882836
The it looks like a problem with the 32" display. Does it work when only the 32" display is connected? Does the device manager properly show the manufacturer and model number of the display?
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Author Comment

by:Abraham Deutsch
ID: 41882891
Yes when only the 32” is connected it works.
Since I have the issue on two computers, two displays, (in different rooms in the school) it would indicate the issue is not the display
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LVL 21

Accepted Solution

by:
CompProbSolv earned 500 total points
ID: 41882897
Are both monitors connected to the same card or to the same motherboard (as opposed to one to a card and one to a motherboard)?

When you are in Screen Resolution and you click on the greyed-out monitor, what do you see in the dropdowns?
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LVL 88

Expert Comment

by:rindi
ID: 41882898
Does the device manager properly identify it?
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LVL 2

Author Comment

by:Abraham Deutsch
ID: 41882915
Not with its "name" but seeing it as a monitor same as with the 20" .
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LVL 88

Expert Comment

by:rindi
ID: 41882922
Normally it should show you the correct monitor model number, unless there is a KVM in between. If it doesn't, then usually it is a driver issue.
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LVL 2

Author Comment

by:Abraham Deutsch
ID: 41882955
Driver from the monitor?
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LVL 21

Expert Comment

by:CompProbSolv
ID: 41882971
I have also seen a bad VGA cable cause the monitor to be indentified as generic, but that shouldn't cause the problem described here.
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LVL 88

Expert Comment

by:rindi
ID: 41882981
No, the Video card. The display should be able to advertise it's specs to the video card using EDID. But for that to work the video card driver must work properly, and you must have a direct connection to the display, as things like KVM's etc often mask the EDID data.
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LVL 21

Expert Comment

by:CompProbSolv
ID: 41883000
@rindi:
If it is not identified correctly, do you think that would prevent both monitors being used at once?  Certainly mis-identification is an issue that should be resolved (especially when trying to set proper resolution) but I'm skeptical that it could cause this specific symptom.
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LVL 88

Expert Comment

by:rindi
ID: 41883009
If the card tries to use a resolution the display doesn't support then the display would show nothing.
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LVL 2

Author Comment

by:Abraham Deutsch
ID: 41883088
Do I understand you correctly, the issue is the card is not enough powerful to support these load. And should be replaced with a more powerful card.
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LVL 21

Expert Comment

by:CompProbSolv
ID: 41883095
"a resolution that the display doesn't support".... good point.  That should be able to be tested by setting some basic resolution such as 800x600 on both monitors.  A problem here is that we've not been told what is shown in Screen Resolution when the non-displaying monitor is selected.  That could tell us a lot.
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LVL 88

Expert Comment

by:rindi
ID: 41883509
It may be a problem of the card, but we would need to know more details on your hardware to be able to say.
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LVL 2

Author Closing Comment

by:Abraham Deutsch
ID: 41887266
One was connected to the motherboard and one to the video card. Plugged in both into the motherboard and both are working. Thank you all for your help
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LVL 21

Expert Comment

by:CompProbSolv
ID: 41887294
In many cases, if you use an add-on card the onboard video is disabled or otherwise non-functional.  If you want two monitors to function you would typically connect both to the motherboard (if it has a second video connector) or both to a video card.
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