Surprisingly Windows 10 started showing “ Windows is not activated. I have clean installed Windows 10 Pro many times (to fresh install Windows 10 new feature updates) in my machine using the same product key and never faced any activation issues. I was using a genuine and activated Windows 10 Professional version in my computer since long time and it was working absolutely fine. After reboot I was shocked to see that my already activated Windows 10 became deactivated. Today I installed the latest cumulative update KB4462933 for Windows 10 version 1803 and restarted the computer to install and apply the update.