I have a HP notebook with Windows 8.1 Single Language 64bit pre-installed. I downloaded the Windows 10 64bit ISO from Microsoft and tried to upgrade from it by mounting it in Windows Explorer and running setup. It asked for a product key and i used a Windows 10 Home generic key which it accepted. After restarted and getting to the Windows 10 desktop, I checked in settings that Windows 10 is not activated. I tried manually activating several times but it keeps failing. I've since restored the computer to Windows 8.1 using the recovery partition and i'm currently downloading Windows 10 via Windows Update. I'm hoping this method will work. Any ideas why the ISO method failed?