Reactivate Windows 10 problem.


I have a pc that I built myself. I installed windows 7 on the computer. The computer was automatically updated to windows 10. Now I have had to replace the motherboard and power supply. Now windows wants to reactivate windows. It fails. I went through all the steps that led me to contact microsoft to reactivate windows. Now they want my windows 7 activation key. I don’t have that. How am I supposed to get that back?