Outlook needs password but dialog box disappears

A collection of various known Outlook fixes for login problems :

• Run Credential Manager, and if your account is listed ensure that it's correct.
  • If not correct, fix it.
  • If correct, try deleting it, reboot and log into Outlook.
• Logging-in into Web Outlook might sometimes show an existing problem such as the need to change the password.
• Start Outlook in safe mode by running Outlook.exe /safe and enter the ids if asked.
• Unlink the Microsoft Account from Outlook
• Disable Modern Authentication by regedit to HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity, create a DWORD item named EnableADAL and set it to zero.
• Under the same registry key, create a DWORD item named DisableADALatopWAMOverride and set it to 1. See Microsoft article.

Undo fixes which didn't help. You might also create a system restore point before starting.

I had the same problem, and given that I have a corporate PC, I cannot do anything requiring admin privileges.

What worked for me: set in the Registry a DWORD value under HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity, named DisableADALatopWAMOverride and set it to 1.

A number of sources that deal with the issue follow. There are a few solutions proposed throughout, with a range of "upvotes".

1. https://answers.microsoft.com/en-us/msoffice/forum/msoffice_outlook-mso_win10-mso_o365b/outlook-password-window-disappears/62cf2b1a-ae26-45fc-95b1-c3c6cce0a188 (the accepted answer, with "28 people were helped by this reply", is the one I posted).
2. https://support.microsoft.com/en-us/help/4025962/can-t-sign-in-after-update-to-office-2016-build-16-0-7967-on-windows-1 (quoted in the first link).
3. https://office365.uservoice.com/forums/264636-general/suggestions/32694751-outlook-is-not-syncing-and-giving-a-need-password (quoted in the first link)
4. https://www.reddit.com/r/windows/comments/7g4tmo/help_outlook_2016_need_password_prompt_wont_allow/
5. https://community.spiceworks.com/topic/2109624-outlook-2016-needs-password-but-dialog-box-disappears

What worked for me on Windows 10 for my work account, no registry needed:

In Windows, go to Settings -> Accounts -> Access work or school, see if your account is listed there, other than the AD account. If so, remove it. Next time you open Outlook it should actually show the login dialog and try to connect.

Screenshot

You might need to try to run an office repair as this issue is caused when the password across the Office 365 suite is not sync'd. Goto Control Panel, Program and Features, right click on Office, click on change and then Quick repair

Alternatively you may try creating a new profile for Outlook as well. This can be achieved by typing mail 32 in the search box of the start menu. Click on New and then create a new profile.