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.
We hope Insiders will continue to test Build 10240, which is only intended to be installed as an upgrade from a previously-activated version of Windows 10 Insider Preview – we do not support clean installs of Windows 10240. 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.
We’re getting really close to the launch of Windows 10, and we’re looking to receive that final bit of feedback before we roll out the finished product!