Many of them installed the latest build of their Windows 10 from some unofficial ISO, they can't activate it. This is because Microsoft has disabled online activation from the release of Windows 10 build 10240 onwards.
Disabling the service will take place until the end of July of 2015.
If you are one of those who are experiencing the same problem after installing Window 10 build 10240, here are some simple steps to do this without having to use third-party tools and cracks of dubious origin.
How to Enable Windows 10 build 10240
Open a command prompt window like Admin.
To do this type in the start search cmd.exe. In the icon that will appear in its results search, right-click and select “Open as administrator”
In the window that opens, type the following command and press the Enter key:
slmgr /ipk W269N-WFGWX-YVC9B-4J6C9-T83GX
Wait until the popup appears stating that the key installed.
Then type the following command and press enter
slmgr / SKMS kms.xspace.in
Again, wait for the popup
Finally, type the following command:
slmgr / ato
After you press the Enter key, Windows 10 build 10240 will be activated.
Activation is not permanent, but it will give you the opportunity to explore the new operating system until the Microsoft activation service works. The activation you performed with the above commands will be lost with the next installation.
Upgrading Windows with the version on July 29 you will be able to activate your operating system normally, since the Microsoft service will work normally.
