Win10 can't be activated? How to deal with common problems

Windows 10 has been installed on more than 110 million devices. It can be said that the free upgrade strategy has helped a lot. But at the same time, there are a few unlucky users who have encountered problems that cannot be activated normally. How to solve it?
Windows 10 activation working mechanism
First of all, we must understand that genuine Windows 7 or 8.1 will be after Windows 10. Automatic activation. This is because Microsoft's so-called "digital authorization" exists in the original system, and it is guaranteed to run Windows 10 smoothly by activating the re-registration on the server. So what you have to do is keep the network open.

of course, piracy can upgrade the system first, and then purchase the upgrade qualifications in Windows Store. If you are asked to enter a product key when installing the system, click Skip.
For boxed discs or digital downloads, you will need to enter the product key. The product key in these packages needs to be kept safe, because Microsoft will ask you to re-enter it when reinstalling the system, even if you have activated the system before.
If you are a member of the Windows 10 Insider project, the product keys that were previously used to activate the Technology Preview are now unusable and they cannot even be used to activate older system versions. If you are joining the Insider preview project now, you will need to upgrade and activate the official version of Windows 10, then choose to get the Insider preview version from the Upgrade Settings menu. (Tutorial)
clean installation

choice if you upgrade clean install, you might run into activation problems. So when doing a clean installation, you need a little trick: you can perform a factory reset and then install Windows 10 - instead of formatting the computer directly - so there is no problem with activation; you also You can upgrade to Windows 10 through standard steps first, then use the Windows 10 installation tool to perform a clean installation after the system is successfully activated.
If you are upgrading from an ISO or multimedia installation media, you can choose to "Upgrade this PC" instead of "Install Now", which ensures that the installed version of Windows 10 matches the version of the system the computer is currently running.
Starting with Windows Insider Build 10565, Windows 10 can be activated directly using the keys for Windows 7, 8, and 8.1. To do this, select Settings > Upgrade and Security > Activation and click Change Product Key.