Running Avast a/v but don't see anything obvious there. Other than that, and a screensaver I've used for years, there's not a lot going on with it. I've recently started running BOINC again after a long hiatus, but that would be counterproductive it it shut the machine down. Other than some kind of error, I can't think of any reason why it would just time out and restart. log out? If so, where is that controlled? This has never happened before. Is there an easy way to tell if it actually rebooted? Something in particular in the Event log maybe? Can they just. I have the power settings on 'never' for when it's plugged in (which it always is at home) and 30 minutes if it's on battery (rarely).
However when I come back to it, it's sitting at the login screen, and when it gets in, everything looks fine except whatever I happened to have had up before, email client, notepad++, etc, is gone and I have to start 'em up again. I am the only user on it, and it's in my home, so I normally just leave it wherever I was when I stop using it for the night or if I'm going out.
Starting fairly recently, my Windows 10 pro T540P appears to either have restarted or logged me out everytime I come back to it after having been away for a goodly while, overnight, etc.