I have the EXCACT same problem with funny enough Vista 64.....It's like the card cant be found by windows and the fan is running non stop on full speed on my card.
I used to have a 8800GTX card installed and that worked fine, But since i got my GTX295 the card cant be found by windows, well it is found but it's not working properly.
Was tinking there might be a connection with that i have a P5E3 Standard Motherboard ??
PLZ help me out guys;)