NEW FIX
The account will not show in the "Access work or School" menu anymore, so instead you need to do the following:
Open regedit as admin and go to this location
Then change the autoWorkplaceJoin value from 1 to 0
Open powershell as admin and run this command
Reboot the machine and go back to the Access work or School menu as below. You should now see the account, disconnect and then re-open outlook to prompt a sign in window
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Sometimes you will have issues signing into O365 when starting outlook for the first time on a PC or when a user has changed their password.
Things like the password box quickly disappearing before you can sign in, or just simply not loading at all. You may also get a message about failing to register the device after using credentials to sign in.
In these cases I have found Windows to be the problem rather than the O365 software.
Try this first (It has fixed everyone I have seen so far)
Type "Accounts" in the start menu search and choose "Add remove or manage app accounts"
Click on "Access work or school" and then disconnect the O365 account from the machine. I would also clear the credential manager of any O365 related entries. Open outlook and try and sign in again.
If this doesn't work try the below solutions.
1. Make sure the device has the lastest version of windows 10 along with windows updates. If windows update says the device is already up to date try using the updater tool - https://www.microsoft.com/en-us/software-download/windows10
2. Now uninstall and re-install the O365 software and try again.
3. If this doesn't work then I have found creating a new user profile in windows fixes the issue. Follow the steps to create a new user profile - https://neosmart.net/wiki/corrupt-user-profile/
Hopefully this should fix the issue without having to do a fresh install of Windows 10
If the information above appears, first try disconnect the network, then open outlook. Then when outlook is opened, reconnect to network.