Where are you entering the licence key? During installation or on the settings screen?
was Win 10 on PC already? If so, click "I don't have a key" or use tab to highlight it on screen and press enter. PC should continue install and reactivate on completion.
If its a fresh install on new PC, use the "I don't have a key" option anyway and we can try to fix activation once win 10 installed.
@fixotip - really? reset is not something I would suggest without trying to figure out another way 1st. Or getting more info.