You could buy a license to 10 and use that to activate it. All your past licenses are based on an OEM (Dell) OS and the keys for those do not apply to Retail or what they used.
So, the idiot I had repair my Dell laptop computer wiped the hard drive and installed Windows 8.1 Professional, even though the COA in the BIOS is for Windows 8 Home.
Not unsurprisingly, Windows 8.1 Professional won't activate. And, it seems that the only way to get Windows 8.1 Home back on the computer is to re-install Windows - something I'd really, really rather not do. I have a Dell disk to do it with if I absolutely have to, but it's a last resort.
I was hoping that installing Windows 10 would save me - since I do have a legitimate Windows 8 COA. No such luck - the upgraded Windows 10 won't activate with the Windows 8 code I pulled from the BIOS. So, I reverted back to 8.1 for the time being.
Is there a way out of this short of installing a clean version of Windows 10? Re-installing all of my programs and losing my stored passwords, etc. would be such a major pain in the butt - I'd like to avoid that if at all possible.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic