It sounds (no pun intended) like you're using third-party drivers that have
been installed either along with your PC or with an installed sound card.
If you have the disk that came with a sound card try re installing the
drivers. If it's something that came with the PC, go to 'Add/ Remove
Programs' in 'Control Panel' and look for a sound driver's / audio entry and
see if it has a 'repair' option by clicking on the modify button.
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Cheers, Tim Meddick, Peckham, London.