Installed win 10 on a new desktop.

I installed Win 10 onto a new desktop (which I built from scratch.) It is a licensed OS. I installed from a current recovery disk. all went smoothly. That is until I needed to put in the license key! Which I did not have (my fault). I thought I could find it in the setting menu, not. I then went to the Windows help, but a lot has changed since the last time. I could not find a help telephone site that I could find information on how to find my license key. I have until the end of March to supply a correct key, otherwise I must purchase a new license key.
I have no problem with Office that installed correctly.
It is bad enough that I must configure my "wife's" desktop, my laptop has Win 11 which I was going upgrade after win 10 was in.

All suggestions welcome.

"Recovery disk"?

Sounds like you're trying to transfer an OEM license (from an appliance PC, like from Dell or HP) to a home built PC.

Is that correct?

I recent appliance PCs, the license key is embedded in the BIOS. However, there may also be a digital license on Microsoft's servers.

It may be possible to activate the new machine using the old license, but I don't know how to do that. OEM licenses are not intended to be transferrable.

Thank you, and yes, both the desktop and laptop were from Dell. If I remember correctly, my upgrade (laptop) came as a result of offers from ME to upgrade to win 10 home. Also my desktop also came as an upgrade from MS. Both upgrades were from win 7. I will check on the rest of your suggestions.

John

Microsoft moves in mysterious ways. At a guess, Windows activated using the digital license on their servers. It's possible that installing 10 as an upgrade over 7 removed the OEM-ness of the license,

I'm glad that you didn't need to purchase a new license.