video card prob: hardware or software

I got an GeForce 5500 with 256 MB video memory. I have installed it on my eMachine W1500(only mobo remains as the original with the cpu). The problem is after my pc was infected with a virus, I did a format on the pc. Upgraded from Windows 98SE to Windows XP Pro. The card is recognized incorrectly and set to default video card settings. Not the settings for the manufactured card. The driver can’t be installed correctly due to the machine saying “It’s already installed.” So… how do I go about fixing my problem?