Lots of things
OS updating drivers causing a re-enumeration of attached devices...
OS updates
OBS updates
etc
I had an externally connected mic (via motherboard connected 3.5mm TRRS cable) all of the sudden stop working a couple of weeks ago.
I had upgraded to OBS v26 a few weeks prior and all had been well. No idea what happened, but I'm suspecting RealTek audio driver did something and changed audio. After a very stressful period of time right before a scheduled live stream, I notice OBS v26 pull down for audio source, changed from Default to the mic, and everything went back to normal. I hadn't changed anythign regarding mic is over 6 months....
so... too many options to bother with why....
Do the basic troubleshooting of outside OBS (I simply use Microsoft Sound settings (control panel) app, and checking that audio is properly being heard (try using Recorder to make sure). Then check OBS default audio devices (personally, I've disabled all of them, and only use selected Audio Input sources). I suspect OBS is pointing to a device, and either the OS or your 3rd party sound s/w changed an indentifier, and you just have to re-associate OBS Audio Input to desired source
This assume of course, that you've done other testing to confirm you don't have a hardware failure
I ALWAYS run my computers behind an auto voltage regulating power source (UPS), with ideal being a pure sine wave version [but that can often be overkill... ymmv]
