How to fix issue with Outlook password prompt disappearing quickly

Situation

The Outlook password prompt appears and disappears so quickly that you are not able to enter your password into the prompt. Without entering your password, your desktop Outlook does not load your new emails and continues to show "Need Password" in the status bar.

Solution

1. Go to office.com and sign in with your Office 365 credentials. Click on the Outlook icon to access your Outlook online. 

2. Check the notifications pane to see if there is a need to change your password. Some organisations have policies set for changing passwords every 30, 60 or 90 days. 

3. Check Outlook online to see if your emails are being received in your Inbox as usual. 

4. Start desktop Outlook in safe mode and try entering the password in safe mode.

5. Disable modern authentication by Registry Editor:

a. In desktop search bar, type Regedit and open Registry Editor.

b. Navigate to HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity and create a DWORD item named EnableADAL and set it to zero.

c. Under the same registry key, create a DWORD item named DisableADALatopWAMOverride and set it to 1. 

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

Credits to Super User