I've already tried two video cards that were recommended by Nvidia and neither one of them worked. Evidently I need a graphics card that was manufactured around 2011 or 2012.
The DH55HC has a Pci express slot. I'm not very knowledgeable about video cards so have been trying to learn more. The age of the Motherboard seems to be the issue. I was told that at some point Nvidia changed some of the specs on their video cards and I need a card that was made before that change which I think was around 2014.