From what it seems, the issue is not caused by Windows Media Player. In order to fix it, check the volume of your speakers, subwoofer and the sound level of your computer. If you can't find the problem, reinstall the sound card drivers and run the Fix Windows Media Player utility provided by Microsoft. If it doesn't help, go to Start > Control Panel, type Windows Features in the search box, press Enter and open Turn Windows Features On or Off. Expand the Media Features list, un-check the Windows Media Player box and click OK. After that, reboot the PC, navigate again to Media Features list and check the player box.
