USB Monitor Works Great. Other Monitor Goes Dark

I have an HP 4520s laptop with an Intel Core i5 CPU, running 32 bit Windows 7 Professional. I have an external moniter connected to a VGA output. When I connect another monitor, using a Plugable USB display adapter, the new monitor works fine, but the one connected to the VGA port goes dark. How can I solve this problem?

Hi Kevin,

Thanks for posting the question! First thing to double-check is that Windows is configured to use all 3 monitors. We can do that through Win 7’s “Screen Resolution” control panel, or the quickest way to do that is to hit the “Windows-P” hotkey on your keyboard.

On Windows 7, this brings up a dialog to allow you to choose between “computer only”, “duplicate”, “extend”, “projector only”. Choose extend to extend your desktop across all three monitors.

If the VGA output still isn’t displaying anything, then next thing to try would be a reboot - each additional screen requires additional reserved memory, and it’s not uncommon to ignore a previous “reboot required” dialog.

If the VGA-attached output isn’t going at that point, we can dig deeper.

Thanks for trying and letting us know - we’ll get all three going.

Thank you!

Thanks for the prompt response. In order to have the original VGA external monitor working, I had Windows 7 display set to “Extend”. Also, I’m
a great optimist, so I re-booted and re-booted without much success. What’s the next step?


  1. My laptop has Intel graphics.
  2. I’ve downloaded the latest (November 2010) DisplayLink driver.
  3. I’ve attached a capture of the screen resoltion control panel.



Hi Kevin,

Thanks for posting this extra info. This configuration should work fine. Can you email contact information to We’ll try to give a call – we should be able to figure out why the 2nd VGA display isn’t being enabled.

Thank you!

Thanks for the quick reply! Let’s dig deeper.

Note that one new thing about Windows 7 is how it maintains a memory of display configuration that is specific to a particular combination of attached displays. So when you have just the original VGA monitor connected, whatever configuration changes you make there (e.g. extending that monitor) are not used when the combination of attached displays changes (e.g. when you add another USB monitor), rather Windows goes back to fresh defaults. Windows 7 expects that new combination to be re-configured, and remembers those settings separately. So then if you remove the USB display, it’ll go back to whatever configuration you had set originally when you only had the one VGA external display attached. Make sense? May or may not be relevant to this problem, but it is surprising behavior that can throw people off…

A few questions:

  1. That laptop model comes with either Intel or ATI graphics. Can you say which one you have?
  2. Do you know what DisplayLink driver version you have? Is it already 5.5 (Sept 29) from…?
  3. With everything set to extend, and both external monitors connected and enabled, what does your Win7 “Screen Resolution” control panel show? Can you use the Win7 “snipping tool” to capture what that control panel is showing, and add that image here? Will look roughly like this:


We’ll be looking primarily to see if Windows *thinks* all monitors are there, or if the one or the other is disabled. Then we’ll try a few things with the settings there to see if we can get things going.

Thanks for your patience while we get this figured out!