it could be caused by th sound card needing to be reconfigured to use the correct audio playback device.
control panel > sound and audio > properties> check for the correct playback.
Or it could be that the codecs are not functioning properly.
K-lite codec pack... it is a free set of video/audio codecs that will allow almost any format to be viewed and listened to.
Free-Codecs.com : Download K-Lite Codec Pack 4.8.5 FULL, K-Lite Codec Pack 4.8.5 STANDARD, K-Lite Codec Pack 4.8.5 BASIC : K-Lite Codec Pack is a collection of codecs and related tools