Trouble Connecting Multiple Display Monitors to OptiPlex 3070

I have two monitors I am wanting to connect to use for dual display. I want to connect them with OptiPlex 3070. The monitor models are E2422H and E2420H. 

OptiPlex 3070 only has 1 DP port and 1 HDMI port. BOTH monitors only have a DP and VGA port to connect to. The monitor I am using to make this post (E2420H) is connected to the computer with a DP to DP cord.  Here is my problem:

I have to connect the second monitor (E2422H) to the computer using a DP to HDMI cord because the HDMI is the only free port on the computer when the first monitor is using the DP port. The computer did not recognize this connection at all. I tested the DP to HDMI cable by swapping it out with the DP cable from the first monitor (E2420H). The computer still did not recognize the connection... I thought it was the cable but this was brand new straight out of the box. So...

Is there a different/better way to test the HDMI port on the OptiPlex 3070 computer? Right now I cant tell if the issue lies with a faulty HDMI port, a faulty cable, or something else entirely (maybe need an adapter?)