Windows 10: I bought a refurbished win 7 pro online but lost the product key

I bought a refurbished windows 7 pro online about six years ago. But I lost the product key and can't find it anywhere. Recently I have to reinstall back to the old windows 7 home laptop and wanted upgrade to windows 10. Without the key screen turned black and can't load any upgrade process. Please help!

:)

 

Lost Win 11 Pro product key

Lost Win 11 Pro product key purchase on an online MS Store

 

Win 10 Pro upgrade using Win 8 Pro product key

I just bought a new computer running Win 10 Home. When I went to upgrade to Win 10 Pro using my Win 8 Pro product key from my old computer, the upgrade wouldn't activate.

Now I'm stuck with a bunch of error messages (mainly 0xC004C003) and am being told windows isn't activated. I can't seem to get my activated Win 10 Home back.

I don't have a product key for the Win 10 Home because it came pre-installed. There's no product code recorded on the packaging or labelling on the device.

So:

How do I either

• activate the Win Pro upgrade, or
• Get my activated Win 10 home back?

 

Win10 home digital license to win 10 pro with product key

Bought a refurbished tablet with a "windows 10 pro for refurb pcs" sticker on it which has the product key.

Tablet shipped with fresh win 10 home install, first thing that pops up on startup is the language screen, ie it's the first screen of a fresh install. It appears to have a digital license on it.

Tried changing the product key to the sticker key after getting through the initial setup, and get a 0xc004f050 error.

How do I change to win 10 pro using the product key?