Some people that I know have had this problem--- v3DMM suddenly loses sound. It happened to me when I silenced 3DMM in the windows audio mixer. I can turn the volume back up, but it flatlines to zero when I select the 3DMM window again.
So, with that, I scoured some threads and found a fix!
Simply download
this .bat file and run it as an administrator. It resets the audio mixer levels and does no harm to your PC.
Thanks to IceCreamMan for posting the script a few years ago, I just put it into a pre-made file for ya guys.