Before you start re-installing Windows, first go into Device Manager and expand Sound, Video and Game Controllers. Right mouse click on your sound card and select Uninstall. If it tells you to reboot, go ahead. When you boot up Windows will automatically detect and install your sound card, unless you have that function turned off under services. If you don't have to reboot, XP will automatically detect your sound card and install the drivers, usually without any input from you. If not, then reboot. If it don't detect it after reboot, then open your control panel and click Add New Hardware and go from there.
However, if XP don't detect the new hardware even after a reboot, or Add New Hardware don't produce any results, then obviously somethings probably wrong with your sound card. Shut down your computer and remove the sound card. Clean the contacts on the card with a pencil eraser, the red ones work best. Re-insert the card and boot up. If the system still don't detect it, then most likely your sound card is trashed.....