Hi there, I'm Tim and will be assisting you today. I have over 15 Years as an Engineer and have been with eBay, DoD and many others. I will do my very best to help you. If you like i can offer remote access and a call.
Did you download the the factory driver?
Odd, so it seems as though it went missing.
Sounds like you have done alot already. Have you tried safe mode to see if there is a diff?
I am not either, just covering bases.
It is possible that hardware died for some reason, this stuff does happen. If it totally stops showing up in device manager then we know its died.
Yes, that's worth a shot.
This came with windows 8.1 right?
No, sorry, at this point i would buy a cheap external USB sound card and move on.