In order to fix the issue, navigate to Start > Control panel > Uninstall a program > Turn Windows features on or off, expand the Media Features list, un-check the box next to Windows Media Player, click OK and reboot your PC. After that, go again to Turn Windows features on or off, enable Windows Media Player and try again to play the movies. If it doesn't work, install Combined Community Codec Pack and try again. Alternatively, I suggest you play the movies using VLC Media Player. It is free of charge and supports all major audio and video formats.