U2417H to Optiplex 790

* What video card/GPU is in the Optiplex 790 computer?
* What video out ports are on the video card/GPU or computer?
* List all monitor cabling attached to the Optiplex 790 and the ports they are using

I apologize in advance if this information isn't correct, as I'm trying to figure out where to find it. I believe the graphic card is: Intel HD Graphics Family. I have a Dell Optiplex 790 with Windows 7 and I can't seem to get both monitors to work. The E2011Ht monitor is connected with a VGA cable and works great. I tried to also connect a U2417H monitor that seems to display just fine until Windows starts. It is currently connected with a USB cord and a mini display port cable. Is there something else I need to do to get both monitors to work, or is the processor (Intel i3-2120 3.3GHz) not compatible? I'm not sure how to know which ports are on the card, but this link takes you to a page with a picture that looks exactly like the back of my computer:

Turn the Optiplex 790 and both monitors off. Disconnect the E2011H VGA cable from the Optiplex 790. Leave the U2417H mDP to DP cable connected to the Optiplex 790. Turn the U2417H on, then the Optiplex 790. What appears on the U2417H?

When I turn on the U2417H monitor, it displays the message 'scanning for signal'. Then when the computer starts, I see Windows 7 start to start up and then goes black when it would normally display the desktop. The monitor then displays the message 'no mDP signal from device', and then enters powersave mode & goes completely blank.

Is there another computer to test the U2417H on?