Last night I tried to install Windows 10 build 10240 (which seems to be the RTM build) by first installing build 10162 which I had already downloaded few days ago. I had to do this because Microsoft wasn't offering the ISO anymore. (If you were trying out Windows 10 insider builds, you had won! I was too careful and I am paying for it now.) Although I could install build 10162, I couldn't activate it hence couldn't update to build 10240 as Windows Update was insisting that Windows was already up-to-date. I knew better.
So I downloaded the build 10240 from “somewhere” (since there aren't any official download links) and did a clean install with the key that I extracted from the tablet. The installation went through fine - no hiccups this time - but I still wasn't allowed to activate it. Same error code as last time.
There is nothing I can possibly do at this point but to wait the remaining two weeks before I can activate it. But I don't know which key I will have to use to activate. I have legit Windows 8.1 key and several legit Windows 7 keys but I don't think I would be inputting those. And I definitely don't want to upgrade from Windows 8.1 or 7, even if they are really clean installs.
I probably shouldn't care too much about this issue. Everything will be answered by the 29th of this month. That's less than 2 weeks away. As long as I won't go into any performance issues in Crysis 3, I don't have a reason to go back to Windows 8.1 for now.
I guess you'll hear a rant from me about the issues in Windows 10 soon. There have to be issues, because you can hardly make bug-free software. I should probably use the tablet a bit and see if it is worth holding onto.