Issue: After upgrading to Windows 10 or installing Windows Updates, Microsoft Office will sometimes deactivate and force you to re-activate in order to retain functionality.
Resolution: Copy the Office activation folder from the windows.old folder to the active Windows licensing store and reboot.
Close all Microsoft Office products.
Locate and copy C:\Windows.old\WINDOWS\System32\spp\store.
Paste the above folder to C:\Windows\System32\spp\store, overwriting the existing folder.
Restart your computer, after which Office should be reactivated.