It’s been a while since I have tried this specifically. My brother is looking to go to a new build (new cpu/mob/ram, but reusing the rest). He has his old win7 oem key, that he upgraded to windows 10. When he rebuilds, is there a way to reuse the old key (just work, or online chat to get it to work, or phone call?), or is over for that key and he needs to buy a new one?