I have not tried this myself but need to due to a conflict with my Sony laptop's bundled program (Roxio's Sonic Digital Media).
Sony VAIO's support suggested uninstalling Media Player 11 via Ad/Remove Programs. Then downloading Media Player 10 from Microsoft's web site and installing it again.
As to not losing your music files, Media Player builds up links to them. There is an option to check that when files listed in Media Player are deleted, that the original files are left alone (i.e. not deleted).
Uninstalling Media Player should not delete your files.
But to be safe, I would back up the folders containing the media files onto an external hard drive anyway.