Windows media player will not play video only sound?

This is normally a codec issue.
You will need to update them as required.
Most of the well used ones can be found here: Codecs.com :: Download latest audio codecs, video codecs, codec packs and tools, FREE!

Personally I hate windows player all together. It always has issues of missing this or that. I use VLC player. It's free, plays any format and never gives me any headaches.

http://www.videolan.org/vlc/download-windows.html