Vista speaker problem

I am running Vista Business on a Dell Dimension C521. I downloaded and installed the sound drivers from dell’s website but I get no sound from my speakers. My volume mixer says that there is no audio device installed, but my speakers don’t have an install, they just plug and play. I tried them out on an XP machine, another dell, I installed the sound drivers for the PC and plugged in the speakers and they worked. Any suggestions would be appreciated.