How did you reinstall the drivers? You need to COMPLETELY remove the old drivers. Uninstall the old ones and then install the new ones.
The fact that it doesn't recognize your card would indicate that you are having 'old' driver issues, the video board isn't seated properly, or your video card is going bad.
You could have a power problem or a heat problem also. Does it crash with the side off an a fan blowing on it? Do you have 16 hard drives and 4 DVD-roms running off the PS?
Remove your old ATO drivers:
http://www.tweakxp.com/tweak1222.aspx