Hoping someone here can help me diagnose the problem with my 12 core 3.46Ghz, 128GB@1333MHz classic Mac Pro 5,1. It is hooked up to six (6) 30" cinema displays via a VisionTek 7870 through 6 mini display ports https://www.amazon.com/VisionTek-Ra...F8&qid=1468148590&sr=8-2&keywords=eyefinity+6. No boot screen, but the system has been rock solid working just fine for the last 9 months or so. The system never sleeps (just the screens dim) and is on 24/7. And the other day, I go to wake the screens and they wont go on. Some are black and off. Some are trying to cycle on and flicker and image and go off. I figure no big deal, it bombed for some reason . Reboot. Same thing. After much dickering, I realize that the card now can only drive 3 of the 6 screens. But weirdly it can drive any 3 of the monitors (so we know they all still work) in any of the ports (so none of the ports are bad) so long as it's not running more than 3 at a time. So now I figure, the card must have went bad, and order a new card, and when I install it. Same exact thing. So now I'm just baffled. I'm wondering, could the power supply somehow be going and not feeding enough juice to the 7870 graphics card, so it can drive only 3 monitors? Could something have blown (a capacitor) on the motherboard? Right now I'm checking to see if I can throw 2 cards driving 3 monitors each in as a temporary solution, but I need this machine for work until apple releases a new mac pro of some kind. Any thoughts on what it can be, or what I should try to further diagnose the problem?