Windows 10: Upgraded to W10, downgraded to W7 unconventionally, won't activate

Could it be that the builder of this custom computer just recycled an OEM motherboard from a pre-manufactured computer and didn't actually mess with the bios?

 

Possibly, but they still need to find the correct certificate to activate it, which makes me think the install was a bit more deliberate.

 

You can still do a standard install of Windows 7, on a PC with an OEM marker, and not use the marker. You just use a Retail disk and type in your key manually. If it's a legitimate key it will activate online. Showkey will still show the marker as being there, it doesn't mean it was actually in use though. I'm just saying. It does sound like something isn't on the up and up, but hard to say 100% one way or the other. Now that being said, if it was an OEM-SLP install, and the key retrieved was the OEM-SLP key, that would explain why the new install won't activate. OEM-SLP keys are blocked from online activation. Like Superfly says, without the custom OEM install media and the matching certificate file, activation will fail. To reinstall Windows 7 with stock install media, you need the key from the COA sticker. If there is no sticker, that's another indication of a fake install. Just Google the last 5 digits of that key and you should know pretty quickly if its an OEM-SLP key.

 

It wouldn't happen to be > Home Premium = RHPQ2-RMFJH-74XYM-BH4JX-XM76F would it. If it is that key is almost certainly blacklisted by Microsoft.