I've had that happen to me quite a few times recently. Though it only just started happening this past year a few times, so I'm not sure why it suddenly started doing it - it's enough to drive me to a Turtle Beach soundcard for crying out loud.
The way I would fix it (without restarting the PC) was to go to Control Panel => Sounds and Audio Devices, and choose the Advanced button under "Speaker Settings." Then switch the speaker setup from whatever you have it on now to like headphones or something else that's different from your current setting. Apply that, then switch back to your real setup and apply again. That always fixed it for me.