nearly everytime it is best to do a reformat when swapping brand of vga cards.
clean install of os & drivers should resolve that fault.
then next time you need to update your driverds follow this:
1) Download driver cleaner
http://www.driverheaven.net/cleaner/ then install.
2) Open driver cleaner then find the option "cab cleaner" then use. This removes the old 27.42 drivers from sp1.
3) Remove drivers from add/remove option.
4) when asked to restart do so but when restart hold f8 then select "safe mode" from options given.
4) When in safe mode open driver cleaner for a second time then select "NVIDIA” then press clean. This removes any INF files windows leaves behind.
5) When complete reboot to normal, if cab cleaner is successful you should get the add hardware window instead of installing above drivers (27.42).
6) Cancel add driver window unless it’s an unzipped & locate file type driver. If it’s .exe type go to #7
6a) Disable any anti virus software.
7) Locate & install nvidia or ati drivers.
Reboot and things should be fine.
Ps after option 5 you might be worth reinstalling dx9.0b and the latest chipset drivers for your mobo.
it would be a good idea to copy & paste this to word then save to a floppy disk for future refernce.