Firstly, you need to know that Windows Media Player 11 is compatible only with Windows Vista, Windows XP and Windows Server 2008. If you're using one of these platforms, navigate to Start > Control Panel > Uninstall a program > Turn Windows Feature on or off, expand the Media Features list, un-check the Windows Media Player box, click OK and reboot your computer. After that, enable the player again. This should fix it. If not, use the contact information from the official web page to get in touch with the support team.