Did you check the Sound Settings to see if the output device was changed?

What kind of receiver?
 
I've had an issue with my Sony receiver in the past where it would display video, but no audio from different devices, such as a Blu-Ray player and a Firestick, but worked fine for other devices.  Switching those to my TV and using passthrough worked fine.  Moving those to a different HDMI input sometimes worked, but sometimes it wouldn't.  The possible solution might be a hard power-off for the receiver (which seems to have fixed it completely on two occasions) but I've not been able to completely figure out what causes the issue.
 
TL:DR - also make sure that there isn't something on the receiver end that's causing the issue.  Try swapping around the inputs or testing other devices on the slot you have the PC connected to.

aylsud5
You are a lifesaver, Lee!  I powered down the receiver (it's a Pioneer) and now the sound is back.  I spent hours messing with the drivers and rebooting the HTPC when it was the receiver that needed to be reset all along.  Definitely, not something that has come up in a web search.  Thanks a million.

Yeah, I feel you there.  Same thing when trying to fix my receiver; no web searches came up with anything.  Just thought that your situation sounded a little similar to what I've gone through a few times (video, but no audio).  Figured that it was worth a shot to rule out the receiver, if nothing else.