Why turn off PC during perezagruski?

When I was sitting on Windows 7, everything was fine and great, going to 10 in early may, 17 years after installation, and further action was selected only shutdown, restart, I didn't for a month and a half, a couple of hours will sit and will shut down, but now, when you restart, it shuts down for a couple of seconds and turns itself, there were such other actions later, but without shutting down, now it's randomly, then stops for a few seconds and turn on or does not have this problem, what could be the problem?