In order to fix the issue, go to Start > Control Panel > Uninstall a program and open Turn Windows features on or off. Expand the Media Features list, un-check the Windows Media Player box, click OK and reboot your computer. After that, enable again Windows Media Player using Turn Windows features on or off tool and try again to open your media files. If it doesn't work, upgrade the program to the latest version. Alternatively, you can open your media files using VLC Media Player, Winamp or any utility from Software Informer database.