I turned off my laptop when it was updating
Windows Update automatically installs important updates as they become available.You can also set Windows Update to install recommended updates automatically or just let you know that they're available.Optional updates, which include updates for other Microsoft products, aren't installed automatically.Windows Update won't add any apps to your PC without asking for your permission, nor will it take away anything you already have.
I haven't seen it lately but it is possible that your problem results from a BIOS conflict with your Version of Windows.
I learned that many people are reporting the same thing (for example, here and here).
It appears that Microsoft is scheduling your computer to automatically update to Windows 10 at a specific time without your knowledge or permission.
We've been getting the annoying pop-up notice on our Windows 7 laptop asking us if we wanted to upgrade to Window 10 for the past year. But on Saturday, my daughter turned on the laptop to do some schoolwork, and then called to me in the kitchen, "Hey Dad, the laptop just shutdown and says it's installing Windows 10. It just happened." I walked over and looked at our laptop, and sure enough, the screen said it was downloading and installing Windows 10 and DO NOT POWER OFF THE COMPUTER.
I didn't want to damage the computer, so I wasn't willing to kill the power.