I just recently (3 days ago) went through the same process and it worked out fine after signing into my re-install of windows 10.
Download the windows 10 image from microsoft https://www.microsoft.com/en-us/software-download/windows10 and follow the instructions for creating a bootable media (in my case, usb flash).
While installing it will provide you the option of entering the key at once or skipping that step. Just skip and continue until you're asked to sign into your microsoft account. After doing that my windows 10 pro is genuine again and behaving nicely!
Hope this helps
