What file did u try to play? It is usupported format error. Can u install VLC player, it plays everything and it does better job than Windows media player. Maybe u just dont have right codec.
And check your program association with files.
Example: .doc file needs MS word or whatever u ar using. But if u accidantally selected play with windows media player, than u get unsupported format error.http://www.filehippo.com/download_vlc/
This will play it for sure, as it is one of 2or3 best players of all the time, and its free and light weight on the system load.
If it will not play than its different issue.