I had this problem. likely a hardware conflict between the sound card/hardware and some other component. In my case I've had it happen with a Sound card and a TV tuner, as well as two sound cards at once. (the audigy sounded like crap, but the generic PCI card was fine.)
Reinstalling the Sound Drivers might fix the issue, or you could try simply removing it from device manager. Then, when you reboot, Windows might give it a different set of resources that will work more reliably. (reinstalling the sound driver would likely be the first thing to do, as stated)