I was out of the room while my pc was bitcoin mining. Last I checked, the temperature for one of the 6990s was at 94C, which is hot, but I thought it wasn't likely to cause damage. When I came back into the room an hour later, the PC was off, and it must've been off for a while because the gfx cards were totally cold. I can't get the PC to turn on again now, despite removing the gfx cards. When I plug the Psu in a light on the mb turns on, so it appears to be receiving power. The only thing iI could think of it being then is the mb itself. Is this a possibility? Is there anything I can try to get things going again?
Do you have a case speaker pluged in to the mobo? If you do do you hear any beeps when you turn on your PC (without the GPU plugged in)?
If you don't have a case speaker do you have another GPU you can plug in to check if it boots then?
If you have neither then I'd go to a local PC parts store and buy a case fan (usualy $2-3) to see if you can get a beep code to help narrow down the problem.
I think odds are pretty good that it's the GPU that died, not the mobo. 94c is 'safe' for the card, it's set to run up to 100c...but it is an older card now and running at that temp on and of over the years could have done something to it.
The PC wouldn't turn on period. It turns out that it's the Psu which is screwed, not the mobo or gfx. It's odd though, because I had 2 6990s in this machine, and a BFG ES 800 Psu powering the PC plus one of the cards, and another 650 watt Psu powering the other card. It seems that both of those Psus are no longer working. That was more than enough power though, and I even had the cards max watt usage underclocked by 8%.