OEM "activate Windows"

Hi All,

I have been attempting to repurpose Dell E7450s that have reached end of life but have encountered an issue with windows not being activated, after reinstalling standard windows 10 and 8.1 on some devices.

The devices originally came with a standard copy of windows, which we removed and replaced with an enterprise edition of either 7 or 10. 

I first attempted to use a Windows 10 USB(created using the Windows Media Creation Tool) and had three successful images. However, after my 4th install, it showed in the bottom right-hand corner that windows needs activating. As the device is OEM shouldn't it have retrieved the Key automatically?

I did a bit of research into the problem and discovered that you can retrieve your key manually using the following command in CMD(as admin)" wmic path SoftwareLicensingService get OA3xOriginalProductKey ".

 When I did this it didn't retrieve anything or give me an error code so I did a bit of asking about and found out that some of the E7450s could have been windows 8.1 originally, so I tried the Dell OS Recovery Media for 8.1 and encountered the same issue.

I  have also tried to find the windows license on the device it's self as I know it used to be located on the bottom of the case or under the battery.

Thank you for any help and sorry about the bad spelling and grammar.