Hello there and welcome to the forum!
Have you tried re-installing Windows Media Player 12? Sometimes an installation can become corrupted during the actual installation process... Also, a couple of good alternatives to WMP are VLC Media Player (available for free), and Winamp (also available for free).. Both of these media players have very good file support and both are very customizable.. Something to think about..
If you would rather just stick with WMP 12 then I would suggest trying to re-install it and hopefully that will solve the corruption issue for you..