I was one of those who tried Windows 8 early and got a Windows Media Center key for free.
Today through Dreamspark Premium I got a Windows 8.1 key.
I normally used my new Windows 8.1 key and Windows 8.1 were activated successfully and because I remembered I had a Windows Media Center into my e-mail archive folder I used it in "Add features to Windows 8".
Windows accepted the key, added Windows Media Center and rebooted.
After the reboot, Windows 8.1 got deactivated and it won't accept my genuine Windows 8.1 Pro key.
I do not wish to format my pc or re-install everything . I just want to activate my Windows 8.1.
I do not care about Windows Media Center, I just want to activate them with my genuine key.