Based on tests I've run, I think I have a bad motherboard and a bad video card.* The Mac Pro is a A1186 model. My motherboard is a 820-2129-A with 3.0GHz CPUs, however I can't find them for sale on eBay. I can find a very similar one, the 820-1976-A for dirt cheap on eBay though. The big question is, will this older mb, meant for 2.66GHz processors, which looks almost identical to mine, be compatible with my 3.0Ghz processors? I saw the mb + CPU compatibility list, but for some reason it doesn't list the motherboard in the table. Instead it just states general models like "Mac Pro 5.1". I may be wrong but that seems way too vague. The Mac Pro 5.1 probably had 5 different motherbaords that it could have come with, each with different compatible CPUs. If that is true, it would seem that the table is not useful to me. *When turned on, motherboard diagnostic LEDs only have "EFI GD" and "TRICKLE" lit up. The video card has both red LEDS on indicating overtemp and bad power. Video card heatsink was clogged with dust so the video card is likely bad. Power supply was replaced without any improvement. A working NVIDIA gfx card was put in instead with no improvement.