O365 user change password then outlook 2016 client prompt blank screen and no response

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 One thing you can try which i often do for licensing office to the correct user. especially if an existing licence is registered to a previous user is the following:

open command prompt as an Admin.

enter: cscript "c:\Program Files\Microsoft Office\Office16\OSPP.VBS" /dstatus

Press enter and you will see near the bottom 5 characters for the installed product. Make a note of these.

then enter: cscript "c:\Program Files\Microsoft Office\Office16\OSPP.VBS" /UNPKEY:

after UNPKEY: enter the 5 characters you observed previously and hit enter.

Now reopen an office product and you will be prompted to enter your users username and office 365 password. This will re-register the product and hopefully resolve your issue.

If you still not getting the authentication prompts id completely uninstall and reinstall via portal.office.com via the users login.