Last night there was an issue with Microsoft's activation servers which caused some people's Windows 10 Pro operating system to "de-activate". If this happened to you, and it is still not reactivated, try running the Windows Activation Troubleshooter, even if you tried earlier. It appears that the problem has been resolved, and running the troubleshooter should fix it if it hasn't reactivated automatically.
If you are having this problem, the Activation Troubleshooter should be showing on the Activation page. Right click on the Windows button on your taskbar (or press the Windows button and X at the same time), click on Settings, then click on Update & Security. Then click on Activation on the left side of the page. On the Activation page you should see the option to Troubleshoot.
