If office fails to activate – possibly displaying a blank logon window or the logon window disappears – use the Office Diagnostic tool found here: https://diagnostics.office.com/#/
The tool must be run as administrator but sign in as the user that is experience the activation issues. Office may activate under the Administrator account instead of the user’s account even though you sign in with the user’s credentials. Follow these steps to switch the license from the Administrator to the User – in addition to the instructions on the following page make sure to log into the Admin Office 365 account online and click to Deactivate the computer from that account: Changing Office Pro Plus Activation Credentials for Windows