Almost the same with me:
Update process went through, I acceptex EULA, typed in my Win8 password and my Live ID and then the process got stuck with the screen telling me "creating account" (resp. simila in German "Konto wird angelegt". After roughly 20 mins. even the display turned dark and I couldn#t wake it up again. Switching off the PC and reastaqrting it made Windows go backt to my running Win8. at least that worked ...