Ok, I also am having a problem with my brand new card (just received it yesterday) and I need some advice.
So I made an upgrade to my PC by buying this card (upgraded from 8800GT) and 8GB of DDR2 RAM. Now the memories are working fine, but this card just can't handle anything. It works most of the time on the desktop, but as soon as more firepower is needed the screen goes dark and the system hangs. It can't even do the Windows Experience Index test. It just crashes, I was able to actually get inside a game for a 1min with some old drivers but it also crashed.
I've tried everything. Flashing to the latest BIOS, a multitude of nvidia drivers, from the latest certified, to the latest beta, to the ones windows update installs, to the ones i can download from gigabytes' site, always using driver sweeper. Eventually it happens with all of them. It's unusable.
Now, here's the crazy part, I installed Ubuntu on my machine and there are no issues at all, obviously Linux doesn't have BSOD, but the card actually works and performs well on everything, no locks, no need to restart X, everything works normally. So I format my HDD, with a fresh install of Windows, just in case that was the issue, but the card goes back to it's crashing ways.
My first instinct was PSU, but I have a 700w PSU and the two 6-pin connectors properly attached, and I don't really have anything much attached to that PSU. It just doesn't make sense.
I'm absolutely out of ideas. Is it possible there is some faulty processor in the card that's causing this, something that's DirectX only? Should I contact the store to get a new card or a refund?