A while back, I changed the internal drive in my laptop and restored Windows 8 using the recovery tools on the installation DVD. After reboot, windows was still activated and everything was working fine. Then I resized and moved the partition on the same new drive and activation was still ok. I just tried a slmgr.vbs /ato and Windows got de-activated! Edit: Tried re-activating but failed with an error code, then tried phone activation, got a confirmation id but when I clicked next in the activation wizard it said not genuine. I had to restore a backup of my data.dat file from Linux and my activation came back. Is this normal? I am using Windows 8 Professional x86 and added the free Media center Pack.
I think that's a problem with WMC Key and installation. Because: Even if you use an real Product Key for Windows 8, at the same moment, you install WMC, the key for the installed Version change to the WMC Key and also the Product ID of the computer is changing. I had the same problem once and had to do a new installation of Windows 8 Pro. While doing that I had a close "eye" on the Activation and was seen the change of the product ID as installed WMC. That changes could have triggered the fail of activation. That also means that it's really adviced to backup an working activation.
The Windows Pro key in this case is genuine. I doubt it could be because of hard drive changes as I used Microsoft's own restoration tool meaning that restoring a backup to a new HDD is permitted.