A colleague at work recently got a second video card–a bottom of the barrel (or close to it) nVidia MX 4000 (PCI). He had an existing AGP nVidia Vanta. Well…the installation did not go well. It did something to Windows so that it consistently blue-screened during the driver load process (the progress bar moving in the startup splash screen).
Windows would start in safe mode, but removing the non-working drivers for the new card did not work. Removing both drivers did not work. Choosing last-known good configuration got us up and running in Windows (finally), but with only the bare VGA driver. Installing a driver from either CD or nVidia’s site ended in the strange error “Access Denied.”
Then I remembered what I had read in Windows Internals about the location of driver configuration information in the registry. Driver info is stored with service configuration in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services.
First we removed all hints of nVidia apps and videos drivers using Add/Remove Programs. Then we went into regedit, into the above key and deleted the keys “nv”, “nv4”, and “nvsvc” (I think they were those, but looking on my own machine at home, they’re a bit different, so I’m half-guessing). I’m sure there are similar keys for ATI chips.
In the meantime, we had found an unused AGP version of the MX 4000 just lying around (no joke), and replaced the Vanta with this. We reinstalled the drivers and everything worked great.