Connecting 2 DP and 1 HDMI monitors to a Predator Desktop (with capability for 3 DPs and 1 HDMI).

zgam10

I recently purchased a Roku TV that I want to use as a third monitor on my Predator Desktop.  The Predator Desktop has 3 Display Ports and 1 HDMI Port.  I am using Windows 10 Home Edition, and a SamSung U28E510 monitor is connected to one DP, a predator XB271HU is connected to a second DP, and the Roku TV is connected to the HDMI port.  The Predator Desktop Windows Settings page detects the Samsung monitor and the Roku TV, but does not detect the Predator XB271HU monitor on a second DP port  Does anyone know how I get Windows 10 to recognize my third monitor?