New
#11
I think there is probably something going wrong with the upgrade that won't allow Windows 10 to activate once it is upgraded if it is even asking for a key... but, you can try this:
Install Windows 8.1 without a Product Key | PCsteps.com
It would be a very interesting survey to know how many people who have activation problems after upgrade were asked for a key during the upgrade and how many weren't. I've upgraded 7 computers via all the options available and have not had a single one even ask for a key to be entered and all of mine have activated with no problems. I am willing to bet that if the upgrade is even asking for a key there will be activation problems after the upgrade - if the upgrade was started from within the old operating system and not from a DVD or USB that was used to boot with.