Exactly what have you tried??? Telling us that you have tried everything you can think of doesn't help us help you..
Have you gone to the manufacturers website for the Sound card or onboard sound and downloaded the specific driver that way?
If its a sound card have you tried disabling the sound card, then removing it, then turning on PC and allowing XP to realize there is no longer a sound card attached, then turn off PC and reinstall card. PC on, and try installation of Driver.