Uninstall Halo and perform a System Restore. The Halo installer should have made a Restore Point from when you installed Halo. Alternatively, go into My Computer, find the Device Manager, and delete the audio device from the Device Manager tree. Reboot. Windows should Find New Hardware and restore your sound. Or, download and install a driver update for your audio. That's in the Device Manager, but you right-click on the audio device, select Properties, and find the Driver tab. Hit the Update Driver radio button.Choose to update only from the manufacturer's web site, not from Microsoft. Those are the best suggestions I can think of.