Hell. I have a laptop running a legit OEM copy of Win7(shipped without install media), and MS Update says it isn’t “Genuine”. The manufacturer advised me to contact MS, and MS told me to contact the manufacturer who again told me to contact MS. It was beginning to be like a civil war among Indians with such a conflict regarding the mutual lack of “tech support”....
This may be a way of escaping this months long clusterf*ck, and I’m a paying customer!
The first time I tried to install 10 over 7, I got an error that the Product ID was not recognized.
The second attempt, I selected the ‘skip’ option when I got to the Product ID screen, and it loaded and installed okay.
What you could do is to download the latest WTP (preview) ISO from a MAC or Linux (so you can get the actual iso), place it on a USB using the Win 7 download tool, and maybe install it on a separate drive, and activate it using the product key on the PC.
Then use the media tool to upgrade it to Win 10. If the WTP is activated them the upgrade should not ask for the product key.