@Arzgania: I have read the entire monologue and have determined that your problem sounds a lot like the one my system is currently experiencing. I have stumbled upon this forum by attempting to find solutions, or rather, confirmation of the cause of the issue I'm currently experiencing. Having said that, I hope this will solve your issue and mine.
My system is a custom build that I put together at least a few years ago. I will tell you that your problem is most likely not related to the PSU because my PSU is a 1k watt PSU and I am currently only using one AMD Radeon 4890. I replaced (at separate times) two Radeon 5770's running in CrossfireX due to loss of video signal on my 52" flat screen. I think both cards failed within a week of each other, which caused me to put in my old Radeon 4890. And yes I did install the correct drivers. I didn't monitor the temps until I was down to just one of the 5770's and much to my surprise the Catalyst Control Center was reading a 99*C temp at idle on the desktop. Sad to say that I saw the no signal display on my tv shortly after that. The fan was cranked up significantly. Obviously, that was the system trying to combat the high temps.
What I'm trying to tell you is that the problem is most likely my motherboard or poor/ insufficient air circulation throughout my case. That is probably yours as well. After I installed the 4890 I opened the Catalyst Control Center immediately after turning on my computer and watched the temps immediately begin to rise after booting into windows. In a matter of 10 minutes or so the temps had passed 80*C and continued to climb no matter what the fan did. Currently, while typing, the temp is reading 92*C with 60% fan speed and 0% activity. The video card doesn't matter here and neither did the drivers. The system shuts off completely after about 2 minutes when I try to run Diablo 3.
And here's what I've discovered: The back case fan isn't working at all. Some time ago it began making a rattling noise and stopped spinning for a brief time. After the fan resumed normal operation I gave no further thought to it. Fast forward a couple of months and here we are. I don't know if that one fan could be able to cause a substantial enough disturbance in circulation, but if the fan isn't the cause of this issue then the only other culprit could be my Asus ROG Maximus ll Formula P45 motherboard. After all, no matter which card I've had installed, I'm still getting the same result. That leads me to believe that the board must be faulty.
Air flow is very important for video cards. They require ample circulation. I suggest you pull the card out. Use some compressed air to blow the dust out of the heat sink fins. Be thorough. check the heat sink make sure it has not been displaced or is missing any screws. Its very important for the heat sink to be perfectly flat along the surface of the chip they are attempting to cool. If a heat sink has been displaced or is missing mounting screws you may need to re thermal paste the GPU, and replace any missing parts. Removing heat sinks can and do void warranty's so be warned. Check to make sure you fan is spinning appropriately. a video card running at 80 degrees C will produce plenty of heat if the video card is circulating appropriately you should easily been the hot air being blown out the back of your card. If physical fan speed confirmed check for circulation obstructions. All those things being confirmed any continued heat issues could be the result of a damaged GPU.
While it may be impractical to take the side of the case off and have a secondary fan blow into my case, it has helped. Immediately after I did this the temperature fell from 91*C to 80*C in a matter of about 5 minutes. However, these temps are still while the PC is at idle in the desktop. The only thing running is my Chrome browser of course. Even when I was running the other two cards in Crossfire I never saw temps above 40*C at idle. I'm beginning to think that it's time for another build and this system can't be salvaged. The motherboard is a P45 after all. So even though I was running a Crossfire setup I was still experiencing a bottleneck because of the PCI express lanes and my slow DDR2 5Gb ram
And after writing this the temps have still only dropped to 78*C at idle. I think there is still something wrong with the system. I'm going to see if the system crashes after I try and run Diablo 3.
It seems your fan might not be functioning right on the video card, be it mechanical (bearings seizing up, coils burnt, or electricity severed), or the video card not correctly telling your fan to spin up (corrupt video card firmware, driver software) Also did you do as i suggested and pull the card and thoroughly clean it?
The fan on all three of the cards that have been installed in this system responded appropriately to the increase in temperature but weren't able to combat the extreme temps that eventually were reached when the system was under load as well as when it was at idle.
The Radeon 4850 that's currently installed is being aided by an external fan but is currently reading 83*C at 34% fan speed. Again the fan speed has decreased since there is an external fan blowing into the side of the exposed case. And again, these temps are while the PC is at idle.
Before this issue idle temps were around the 35*C - 45*C range while at idle and didn't increase much when under load. Since this problem persists no matter what card has been installed there must be an underlying issue being caused by something other than air circulation.
Do you know of any other reason that the temperature would rise so quickly while at idle?