Just an update.. possibly your no sound issue is speaker related.
For example I have 7.1 sound speakers.. after testing them in control panel I found 2 of them werent working so set it to 5.1.
Additionally I plugged in my Headphones leaving it as 5.1 and couldnt hear walking or speech...
Well not sure about the "no sound" but know my radio music was so quite I had to turn my speakers up to full just to hear the music with the speaker against my ear.
I still have a ringing from when the DJ came back on and blew my eardrum out.
Anyway looked into a cause, Alt-Tab was...