I would guess you bare correct that the problem is with the PC. The spec you give shows the possibility of an internal on-board graphics chip and an Nvidia card. Which is the case for your machine. If you have the Nvidia card installed then it could be that causing the problem. Can you remove it and switch to the on-board graphics. (usually need to select this in the BIOS and connect the cable to the onboard monitor socket).
iMac Pro review