If you are seeing the “Activate Windows” watermark on Build 10240, please first understand that all pre-release product keys published earlier for builds of Windows 10 Insider Preview have been deactivated and will no longer activate any Preview builds, including Build 10240. This will not impact any devices that were activated in the past using those product keys. To check your activation status, go to Settings, choose Update & Security, and select Activation.
There are steps you may be able to take to solve your activation issue, depending on which edition of Insider Preview you have installed.
Windows 10 Insider Preview, Enterprise Edition
You’ll need to activate with your organization’s Volume License keys (KMS or MAK) or VL keys acquired through MSDN subscription. Please post any questions related to Windows 10 Enterprise Insider Preview in the TechNet Forum.
If you installed the Enterprise Edition, but are not part of an organization with a Volume License, you will not be able to activate. Please revert Windows 7 or 8.1, and upgrade to Windows after it’s released on July 29 by reserving your copy of Windows 10.
Windows 10 Insider Preview, Home or Pro Edition
If you activated the Windows version or Insider Preview build you were on before Build 10240: please wait a few days. A very small percentage of devices may experience a delay in activation.
If your device has been connected for a few days and is still showing the watermark, you probably didn’t activate your previous version before upgrading to Build 10240. Please revert Windows 7 or 8.1, and upgrade to Windows 10 after it’s released on July 29 by reserving your free copy of Windows 10.
Please note that Windows 10 is intended to be installed on Genuine Windows devices, whether devices in the Windows Insider Program or those taking advantage of the free upgrade offer.