The Timeline to register for Windows insider to be apart of the Windows 10 PC program has closed off since June, only windows mobile remain
Windows XP users or anyone who want to use windows 10 by using the Insider program can't anymore unless they have already signed up and got a digital signature for their hardware computer.
All previous build have been removed, and the same keys won't work unless they are on the latest or the previous build.
Windows 7 SP1 and Windows 8.1 users, time to get genuine to enjoy upgrades to windows 10 free.