Short story since I tend to write a lot: 2008 mac pro will turn on for half a second with GTX 285 hooked up, and then turn off. I put in an old 8800GT and it boots fine. Is this most likely a problem with the GTX285 (my guess) or could it possibly be the power supply? I have a 2008 Mac Pro (8 core) with the following: GTX 285, EVGA Brand (the way overpriced retail official Mac version) 2x optical drives 8x 1gb sticks 1x SSD, 3X hard drives I dual boot into Windows to play games - not the best gaming rig but it works well. The other night I left it booted into Windows, and in the morning the machine was frozen. I turned it off, and then back on - the power in the room would flicker, the mac pro would turn on for half a second and then turn back off. Long story short, it finally booted when I unplugged the two power cables to the 285. If I plug only one cable in to the port furthest from the back of the mac, the computer doesn't turn on still. If I plug only one cable into the port closes to the back of the mac, the mac turns on but doesn't boot. I have switched power cables, and the cable doesn't seem to matter, and I tried both cables with the 8800GT (it only requires one) and the mac booted fine. I am guessing the video card is most likely to blame, but I also wondered if it's possible that the power supply is going bad and can no longer output enough power? I disconnected all drives except for the SSD since they're the only other thing probably drawing a lot of power right on boot, and even with just the SSD plugged up the problem persists. Can I put the Mac GTX 285 into a PC and try to boot it to see if that is the problem? Will a PC boot with it hooked up? And a follow up question assuming the video card is indeed the problem: What is the best card to get for a 2008 Mac Pro that I can power off of those two cables? Thanks so much for any advice.