I originally had genuine Windows 8 64bit version on my desktop. Then I installed the Windows 8.1 Pro Preview version. Now I am unable to upgrade to the full windows 8.1 version. I tried reverting back to Windows 8 but that didnt work either. Even when I try to install from windows 8 installation disk, it failed and went back to Windows 8.1 Preview. Can I get help? Thanks a lot.