Wow, people really don't grasp the context written in posts, do they?
You used the disk that you got with the gfx card? I would download and install the latest driver available from nVidia. Also, if you didn't already do it, be sure to install the latest directX version. Formatting and reinstalling windows probably installed an old version of directX.
If it is an older PC, I've found that I had to turn the hardware acceleration down a click (desktop properties>settings tab>advanced>troubleshoot, there is a slider for hardware acceleration). You could have had this turned down before and it defaulted to full after the reinstall.
Reinstalling windows will put a crapload of garbage in your process list. You have to disable all that crap that windows starts up. Most PC's and/or windows installations out of the box I've seen with 40-60 processes running. I have mine cut down to 21.
Just a few things, I'm far from an expert. But apparently more of an expert than Compaq's "expert" technicians since I had a framerate issue when I bought mine and all I could say when I talked to their technicians is "Already did that. Already did that too. Been there done that...." No help whatsoever they were.