I have a Windows 7 and a Windows 10 computer.  Each has a program called Share-X , each have Nvida graphics and Realtek sound.

For a long time Share-X would capture an area of the screen as well as the sound, handy for grabbing a bit of a YouTube video.  Now both computers give the error message that the virtual sound can't be accessed.  I can no longer run Share-X to grab a screen video.

Audacity can record the sound from a video and from a mic, sound play on the TV in my computer.  Nothing else seems affected by whatever the problem is with Share-X.

I've reloaded sound drivers, I've removed Share-X and re-installed it.  I've run multiple diagnostics and 3 different anti virus programs (in safe mode too) and nothing shows up.

If it had just happened on the Win7 computer I'd believe that something changed but it's the same on both and I seldom use the Win10 computer for anything but email and browsing.