Try VLC (free player with built in codecs) & plays everything except the odd wmv file (choose the nearest mirror site.) Its controls are not the best but it works with the most recent formats out - so it's effective!

Check also you have the most recent codecs: http://www.divx-digest.com/software/nimo_pack.html (choose mirror2 link only!) or http://www.k-litecodecpack.com/