It should be said that Windows Media Player 12 is compatible only with Windows 7, Windows 8 and Windows 8.1. If you're using one of these platforms, you can download the program from the official web page. Since it updates to Windows Media Player 11, it means that you use Windows Vista or Windows XP. In order to fix the sound problems, go to Start, type dxdiag in the Search programs and files field and open the utility. Click the Sound tab, check your sound card model and download and install the latest drivers available from the developer's web page.
If it doesn't help, right-click the Sound icon from System Tray and open Playback devices. After that, right-click anywhere in the Playback window and check the Show Disabled Devices option. Double-click on your device and select Enable from Device usage. Click Apply, OK, select again the device and click the Set Default button.