I never used to use WMP, because of the lack of extensions it could play. So i downloaded GOM. It was good, but i prefered the simplicity and look of WMP.
One day, i came across this: Media Player Codec Pack - Free software downloads and reviews - CNET Download.com, it's an excellent install, making it able to play nearly anything with Windows Media Player. I now use it again

I think it patches your system or something, but check it out properly before installing.