Firstly, please confirm you have 64-bit Windows by right-clicking Computer in the Start Menu and going to Properties. I'm not doubting you, just double checking before we proceed.
Are you sure you selected the following from the Download Drivers section at NVIDIA's website (for your motherboard, firstly):
- nForce
- nForce 6 Series
- nForce 650i SLI (presuming you have this and not the 650i Ultra)
- Driver
- Windows 7 64-bit
- (your language)
I'm using the 780i SLI nForce motherboard and the 280GTX and had no problems with either installation.
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With regards to your video card, please confirm you chose the following from the Download Drivers section:
- GeForce
- GeForce 200 Series
- GeForce GTX 295
- Windows 7...