I activated my Win 8 Pro using a retail key (Not bought ! ) which worked fine. I then decided to add the WMC using the free key sent by Microsoft. When I entered the key in 'Add Features' it confirmed that it worked and started the install. One installed I checked activation and my system was no longer activated which I found strange when it had accepted the key when installing. I then attempted the phone activation but the free key was not recognized. I then 'downgraded' back to Win 8 Pro but wondered if anyone managed to get the WMC to work using the free key with an already activated Win 8 Pro ???