An issue with the internal PCI sound card
This just happened to me again, and it made me think of your problem. In one of the computers I have set up, it has 4 internal sound cards as well as several USB sound cards. I record and locally stream everything but only send two of the streams to the public......
It first happened when I was away for a few days. When I returned I found the sound level for one of the PCI cards to be "very hot". I merely opened up the mixer changed the level, and ended up putting the level back to the same spot. It seems like the card "forgot" where the setting was.
I wondered what made this happen. Nothing else had changed. I had recordings to show when it happened and I could see the amount of the level change. The computer is on a UPS and so I know it had not rebooted/etc.
This has now happened 4 or 5 times, once just this week. The sound was very hot so I opened up the mixer, moved the pot down and back to the same spot and now all is "OK"......
SO, perhaps all you need to do is something with the mixer or audio setting via Windows. It could be an issue with the sound card. Perhaps we even have the same model of flakey card.