Windows 10 doesn't shut down or update

I have had a frustrating and a little bit scary problem with my Windows 10 pc for almost a month now. When I try to turn off the computer, it starts closing and the screens go black. But immediately after they start again and the lockscreen comes up. The only way to shut the pc down is force shutdown, by holding the power button for a few seconds. I'm scared for my hard drives every time. As far as I can tell, restarting looks normal, I get the mobo logo and bios stuff, and everything is normal. On shutdown I don't get the motherboard or windows stuff, just goes straight to lockscreen. Fans sp

Question by eemil on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.