Windows 8 activation with WMC

I have downloaded and successfully installed Windows 8 with Windows Media Center.

I had also previously obtained a serial key for Windows Media Center11 from Microsoft via email.

Is there a way that I can now use this WMC serial key to activate Windows 8 and, if so, how do I do it.

I have tried following the guide given by numerous people where you go into Search and insert "add new features" etc. but this doesn't work for me because, presumably, I already had WMC as part of my downloaded Windows 8 package and so I'm not getting the option to add a new package.

Thanks for any help.