Windows would not boot and automatic recovery failed so I formated the Hard Drive and re-installed Windows 10 Pro from Microsoft Windows 10 Pro CD (aka not specific to HP). I left the CD Activation Code blank during the install, since there is no Product Key stick attached to the device.
When I try Activating Windows I get error code: 0xC0048100 basically saying that Product Code is bad.
It is my understanding that product code is somehow imbedded in the motherboard and typing an actual code is not required for Windows 10. After Windows 10 is successfully activated once you can re-install windows multiple times as long as there isn't any significant hardward changes (I've made none).
Since Window's 10 was running fine for several month why won't it activate now after fresh install?
Yes Windows 10 Pro was orginally installed (only option for HP Pro One 600 G2 ). It does come with "Windows 7 downgrade rights" but I never exerised these options. Windows 10 Pro was activated before doing the fresh install.