did you uninstall the onboard vga drivers in safe mode ?
then install the video card , then start up going straight into the bios (del ) key and disable the onboard video ?
also set your agp port and bios setting to reconize new hardware along with the graphics size AE 64,128,256 ? now restart then load up the drivers for the new card , then run dxdiag (9.0c) you should be good to go then .
note you may have to turn off any AV /firewall junk to get a clean driver install.