Didn't Microsoft tie your machine license to your Microsoft account for this reason?

OEM licenses can be kind of funny. They aren’t portable, though I would’ve thought that the motherboard was replaced by a motherboard by the same OEM, etc. and should’ve qualified to use that OEM’s license.

It does, or at least it used to. Back during the Vista days my copy of Windows failed to activate after I replaced the motherboard, but Microsoft support was happy to help me when I explained that it was the same computer with new parts in it.

People who like their Windows license to be activated after a motherboard replacement, it seems.

Then again, the manufacturer probably should've made sure the replacement motherboard was covered by a license.

From my experience with Lenovo if the motherboard got replaced by the manufacturer they should have given you one with a license attached

What did Microsoft tell you when you attempted to reactivate? It used to be they'd just do it if you called them.