Verified answer

try opening your standard diagnostic tool and see if everything is working. i think i had the same problem but i fixed it using that.

Click on the speaker icon next to your clock or go into 'control panel' from the start menu and pick 'sounds'.

Open up the mixer, and you probably have something muted or turned all the way down - windows lets you leave WMP playing without having to listen to all of those annoying bleeps and bloops.