The motherboard is an HP ATX board, model PCLDV0GD62R9LT. It has two DIMM slots, one 16x PCI Express port, four PCI Express ports, four integrated USB 2 ports, USB 3 capability, gigabit ethernet, dual DVI video out, dedicated audio out ports, and four SATA connections.

This motherboard also has a Mini PCI Express slot, which originally wasn't filled. I added a Wifi module that I swapped from another computer, and it works.

You could probably add a discrete GPU in here using the 16x PCI Express slot, but you should consider the PSU's limitations and other factors before choosing one.

You can find the motherboard info in the orange circle.