3900PDZ/Alienware Laptop doesn't recognize 3rd external monitor

Alienware laptop with 3900PDZ docking station, 2 of 3 external monitors recognized. All monitors previously worked on an HP Zbook. All windows and system software up to date. No change in configuration on docking station, software for docking station downloaded and installed on Alienware laptop. Simply won’t recognize 3rd external display. Would love some thoughts. Thank you!


Thank you for contacting us, I am sorry this is not working as expected and I am happy to help!

This docking station relies on two graphics technologies to support up to three external displays.

The “HDMI 2” and “HDMI 3” outputs are controlled by DisplayLink USB Graphics Technology, this is a combination of software on the computer and hardware on the docking station which extends the capability of the computer to support more displays than the computer was designed to support. This requires installing the DisplayLink drivers for Windows ( https://plugable.com/drivers/displaylink ) or the DisplayLink Manager App for macOS and configuring macOS to support the external displays ( for macOS 13 and 14: https://kb.plugable.com/1595423, for macOS 11, and 12: https://kb.plugable.com/1185378 ).

The “HDMI 1” output relies on the computer’s internal graphics controller, it utilizes USB Type-C DisplayPort Alternate Mode (“Alt-Mode” for short). This is an optional USB Type-C port feature which is not enabled on all computers. This relies on the computer’s built-in graphics drivers and requires the docking station to be connected directly to a USB Type-C port with Alt-Mode capability using the original USB Type-C data cable provided with the docking station. USB Type-C cables from other products, or purchased separately online may be charging cables that do not support Alt-Mode video data.

I recommend we start by verifying the docking station is connected directly to the computer using the original USB Type-C data cable provided with the docking station, this cable is about 3ft long, black, with black plastic molded ends. Each molded end has two small holes about 3/4 of the way from the USB Type-C connection to the strain relief, pictured below to help identify the cable:

USB Type-C “Charging” cables, adapter cables, or any devices between the docking station and computer will block the USB Type-C DisplayPort Alternate Mode video data and prevent the “Display 1” connected display from being detected by the computer.

I also recommend we confirm if this system supports USB Type-C DisplayPort Alternate Mode video output, please let me know the specific model of Dell Alienware notebook computer:

  1. Open the Start Menu and search for “msinfo32” and launch the first search result
  2. Please let me know the values from the following entries ( on the right column ):
    2a) “System Model”
    2b) “System SKU”
  3. Please feel free to attach a screenshot of this window to your reply email if you prefer by using the Windows Snipping Tool ( from the Start Menu search for “Snipping” ) and I can get the details from there

I will look up the system specifications to ensure this computer supports USB Type-C DisplayPort Alternate Mode to enable the “HDMI 1” output on the docking station.

Thank you, and I look forward to your reply.

Plugable Technology

Well I am mortified! I picked up a usb male to usb c female adapter because apparently I was too lazy to thoroughly look over my laptop (thinking it didn’t have a usb c port). So after the adapter purchase and no recognition of the 3rd monitor, I finally shut down my system and looked at the back. Sure enough, there was the usb c port. Plugged in the cable from the docking station and VIOLA!! All is well and now I must wear the tech dunce cap of shame. (A completely horrifying look for someone with a degree in IT. Sometimes we simply don’t think of all the little things first.) LOL Thank you for so quickly responding and hopefully my dingbat post will help others before purchasing any additional equipment OR make a total fool of themselves. Thanks again!!


Thank you for replying back to let us know that everything is working as expected now and providing this resource for other docking station users!

Please feel free to open a new thread if you have any additional questions, or to contact our support team directly at ‘support@plugable.com’ if there is anything else we can do to help.

Have a great day!

Plugable Technology

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