Upgrading mobo/cpu, how do I keep free Win10?

[Dezeria]

I'm replacing a motherboard, cpu, ram and graphics card in a PC, so basically it's mostly a new system. It ran Windows 7(retail dvd) before, but used the free upgrade to Windows 10 when it came out.

As far as I can tell, It takes your Win7 key, and uses that to make a Win10 license, but you cannot move that Win10 license to a new PC. So I'm wondering, how to I get my free Win10 on the "new" PC? Can I just install Win7 again and get a new upgrade, or will it not work since I did it with that Win7 key already before?

Any thoughts? Upgrading is already pricey, I want to use Win10, but don't want to buy it if I don't have to. Please no "stick with 7" replies.

[Denpepe]

if you can get win 7 reactivated it should work, did for me (just took an automated phone call to reactivate).

[Butler to Baby Sloths]

When you get to activating it, if it doesn't do it automatically you go to the "activate by phone" option and talk to the robot.