@Chris. At this point I'd call it the motherboard but you changed that too. " I've switched out the hard drive, motherboard, power supply, processor, and graphics card "
Some folk keep their old failed cards, boards and more and then try again later. It ends up in the shop and we find a PC with bad everything. The cost to repair is too much compared to starting over.
Point? Folk have done this and it's a mystery why since the shop fees are pretty steep.