Sounds either like a codec issue or the idiot hasn't encoded with the sound (I've come across that ... they were obviously inexperienced at encoding.) Might I suggest you try xtra codecs such as either 1. http://www.land.ee/d_nimo_codec.html or 2. http://www.free-codecs.com/ OR get a backup player with built-in codecs like VLC: http://www.videolan.org/vlc/ (choose nearest mirror site) & it's free.