There are no active mixer devices

I found a fix!

I had this problem as well. It happened randomly in the middle of downloading music.
But thanks to some tech help from another site, the fix was pretty easy.

Go to Start --> Run, and type in services.msc.

A window will pop up with a list of services. Scroll down to Windows Audio. Right-click
and click on Properties.

Make sure that "Startup type" is set to automatic. Also, make sure, under "Service
status," start is selected. (Mine was somehow set on stopped. I clicked start and
-- voila! -- it worked.)