I don't know about you guys, but I never upgraded to Windows 8.1.
Since my sounds stopped working due to updates, I DID upgrade my Surface one to Windows 8.1 and now it DOES work. Just thought I'd share.
I have had the same issue. If I restart my surface it will work for a little and then stop.
I use Rosetta Stone and when it stops working, Rosetta stone also stops working and says there is no audio output device on the computer.