you can use this procedure to uninstall the core of Windows Media Player.
Click Start, click Run, type %windir%\$ntUninstallwmp11$\spuninst\spuninst.exe, and then click OK.
Click Next, and then click Finish.
Or
go to Computer right click on C: /properties. Select Disk Cleanup and then click More Options. Select Windows components and find Media Player in the list. Remove the check from the checkbox and than click OK.
To re install do the steps again, this time check the Media Player box and it will be re installed. it will probably request the Windows CD to complete.