Hello,
Did you solve your problem ?
I have the same problem and it is impossible to install Win 8.1 from the Store.
I have a nvidia nforce 630i and on some topics, they say that Microsoft doesn't support this motherboard.
Have you got a solution ?
No not yet but I am going to attempt some of the methods on this thread when I get the time.. It's an absolute scandal that we have to go to these lengths.