I suggest you to download latest k-lite codec pack. If that doesn't do it, try this free player VLC, it's quite popular and I am using it myself. It plays literary anything. Hope this helps :)
I believe for a dvd you need a variation of a mpeg-2 codec. These can be found online by themselves or also contain in large codec bundles. There are also stand alone player that don't require a codec for dvd playback.
You should use VLC media player. It is free, and can play discs from any region. However, you can't use it with windows media player, you need to use its own UI. Just google VLC for their website.