If the problem is not the video file then it might be a CODEC issue. Get update codecs from any of these locations: 1. http://www.land.ee/d_nimo_codec.html 2. http://www.free-codecs.com/ 3. http://lists.gpick.com/pages/CoDecs.htm 4. http://www.k-litecodecpack.com/
Also consider getting a backup player like DivX or VLC (in-built codecs): http://www.videolan.org/vlc/ (choose nearest mirror site)