That happened to us, and what followed was a 8 week nightmare.
1. My son's school MS account took over his private account, only because he linked the two accounts.
2. Suddenly my son's Windows said it was un-authorized.
3. We called Microsoft, they could not fix it.
4. We called the manufacturer of the machine (they shipped Windows as OEM). They could not fix it.
5. Called MS again. They gave us a new activation code. Did not fix it.
6. Called MS again, this time they said to reinstall Windows (This is not a joke).
7. Upon re-installing, Windows would not activate. No error message, no nothing it would just hang in the activation loop.
8. Called MS. They had no clue. Claimed H/W issues.
9. Called manufacturer again. Also claimed H/W issues. I said that I can access the internet from the machine while it was hanging in activation, so network was not the problem.
10. Manufacturer sent someone out (I had bought warranty). He switched the SSD with a new version of Windows... The did exactly what I did. Same problem, would not activate.
11. Some back and forth with MS and the manufacturer involving many reboot and (I kid you not) turning off all wireless routers... MS still would not activate. Manufacturer (and MS) did not believe me. So they sent someone again. Did the same thing, again. Did not work.
12. Manufacturer said I needed to send in the machine. So I did. I included a note about what the problem and to please not just re-install Windows, because the activation was the problem.
13. Got the machine back... They had just re-installed Windows. Would not activate.
14. Started to get upset. After some pressing manufacturer agreed to send a new machine.
15. First they sent someone out again. Did the same thing again. Forced me, again, to turn all wireless routers off, so that (he claimed) Windows would activate without network. Again... Did not work. Activation just hung.
16. Eight weeks into this we ended up getting a new machine (yes, not kidding) from the manufacturer and now the same version of Windows (from the same memory stick) on the same hardware, same drivers, all the same, would happily register.
I cannot even begin to express how annoying and useless this was. And MS and manufacturer were helpless and useless.
Personally I have stopped use Windows over 2 decades ago - only using Linux, but my son wanted a gaming machine, and so I relented. :)