Windows 10: Has anybody had this happen with a Windows 10 PRO OEM?

So I purchased an OEM key that arrived completely unopened and in the official Microsoft Windows 10 Pro sleeve. I inspected it and it legit looked it was never touched and had all untampered seals.After putting together a new build for my daughter, I was getting an issue saying that Windows cannot activate due to hardware changes. Now this is a completely new build that had no previous installs. I called Microsoft to get help manually activating it and they informed me that the key I purchased was legit but for Windows 8.1 despite it coming in a Windows 10 package.Outside of asking for my mone

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Windows 10 pro

I need to change my motherboard, have windows 10 pro. When i google how to it says go to activation then add an account, my issue is there is no add an account option under activation? Or am I in the wrong window?



Not sure how to proceed, ive googled it and the same results. Do I have an OEM or? On the disk sleave it says OEI DVD?
The COA says windows 10 pro for OEM software

 

my windows 10 oem didn't come with a product key

Dude, go to Newegg right now and read the questions and answers tab on Windows 10 OEM. The OEM copies that are listed there DO in fact, come on an optical disc. The flash drive ONLY comes on Retail copies.

 

Windows 10 serial on OEM


So I'll summarize steps made...

1. Saved serial number (taken with Belarc Advisory) from preinstalled (half chinese language) Windows 8.1 (don't know exactly the version, suspect Windows 8.1 with bing) on tablet
2. Formatted tablet
3. Tried to make a clean Windows 10 (HOME, HOME N and also PRO, everytime with the same result) install with ISO taken with MediaCreationTool, during install (and also after completing installation) it says that the saved serial is not valid
4. Tried to reinstall Windows 8.1 (ISO taken with MediaCreationTool again) HOME, it says that the serial is not valid

So i suspect that the saved serial, is from a WINDOWS 8.1 WITH BING OEM version and this kind of ISO is not accessible/downloadable anywhere (at least I can't find it, any suggestion?)

Still not tried SHOWKEY with that serial, I am in office now, and the serial is saved on a usb pen at home, will try this evening.

So I'm stucked but if everything is like I suspect, it's incredible. If I have a tablet/notebook/netbook with Windows 8 preinstalled, it seems that I can update to Windows 10 without problems, but if I want to make a clean Windows 10 install that serial is not valid...