I had the exact same problem, and none of the solutions worked! I'm running from my laptop to TV via HDMI, and the sound usually projects through the tv once I plug the cable in. The solution I found was to open the Device Manager, and down at the bottom of the list, under system devices, I found that the High Definition Audio Controller was disabled, mysteriously and on its own! I enabled it, and VOILA, the audio was immediately transferred to my TV! I have an external speaker system hooked up to my TV's audio output, so now my laptop is working on a bigger HD screen w/premium stereo sound!
Start Menu - Control Panel - Device Manager - System Devices - High Definition Audio Controller - right click - properties - enable
Hope this helps!