|Something similar happened to someones PC that I diagnosed and was able to fix. He basically had Skype installed, and for some sgtrange reason the computer would place a call the hang up, then call then hang up. anyways to fix the issue of sound muting i just turned off the feature of 'Mute on call' - could be the same on your machine, no harm in trying i guess. here is how|
Under control panel click on
Sound >> Click on the Communications tab. Then from there
select the 'Do nothing' option.
Hit Apply then Ok
Hope that helps,
Please return with your results :)