I have a USB monitor and a HDMI monitor - each of them work fine when plugged in by themselves. However, when I plug both of them in, one will stop working. As soon as I unplug one, the other will start working.

What could be the problem ? All three (laptop's built-in, the HDMI and USB one) appear in "Display Settings".

  • Laptop: Acer Aspire S3, i7-3517U
  • USB monitor: ThinkVision LT1421
  • HDMI monitor: LG, IPS, full HD
  • What laptop model is that? Or what CPU does it have? Monitor models could be useful too. – gronostaj Oct 21 '15 at 8:04
  • @gronostaj, added more info – Mihai Rotaru Oct 21 '15 at 11:13
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    I always thought USB displays had their own processor so shouldn't count against the GPU's maximum display count. Curious – Journeyman Geek Oct 21 '15 at 11:23
  • @JourneymanGeek: That's how I understand it too - plus his GPU supports 3 simultaneous outputs anyway. – qasdfdsaq Oct 21 '15 at 11:32
  • Just because the display is USB doesn't mean the CPU is not helping to drive it - check out displaylink.com/for-business/common_questions.php. – David Vernon Oct 21 '15 at 11:35

I will assume you have doubled checked that correct drivers are installed for the USB monitor!

This sounds like it could be a simple control panel fix.

Have you tried

a) Plugging in both the USB and the HDMI monitor, then Identifying the monitors in the control panel

b) Making sure the 'Display Settings' is configured to extend the desktop over all 3 displays, not just 2 of them. Steps for doing this can be found here: http://www.intel.com/support/graphics/sb/CS-033714.htm

c) Making sure the extra graphics driver configuration software from Intel (used when driving the displays using the Intel graphics) and NVidia (used when driving the displays using the NVidia graphics) are configured correctly.

d) Finally, seriously consider upgrading to Windows 10, which bring DirectX 12. DirectX 12 allows for far superior handling of multiple displays, including the ability to push more work to your laptops more powerful graphics card.

Update: Sorry, missed the question title saying you were already running Windows 10: It is worth making sure every display driver you're running (Intel / Nvidia / DisplayLink USB) supports DirectX 12

| improve this answer | |
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    He's already running windows 10. – Journeyman Geek Oct 21 '15 at 11:33
  • I may be having a bad day, but I just reread this and can't find anywhere where he has referred to Windows 10? – David Vernon Oct 21 '15 at 11:42
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    Title and tag. Its an excellent answer otherwise. – Journeyman Geek Oct 21 '15 at 11:42
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    I didn't configure the extending options correctly in Display Settings. Working nicely now; thanks David ! – Mihai Rotaru Oct 21 '15 at 16:10
  • In my case, I have an HDMI and RGB output. Adjusting the multiple displays in the Intel HD Graphics Control panel also solved my woes. – Brett Oct 22 '15 at 16:26

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