Follow these steps in order.
- Force-close Outlook
- Right-click Start and select Task Manager.
- Select Microsoft Outlook, then choose End task.
- Confirm Outlook is fully closed, then close Task Manager.
- Clear the new Outlook sign-in/cache data This often fixes sign-in loops and launch problems.
- Close all Microsoft apps (Outlook, Teams, Word, etc.).
- Press Windows + R, type
appdata, and press Enter. - Go to Local > Microsoft.
- Delete these folders if present:
-
Olk -
OneAuth
-
- Restart the PC.
- Try launching Outlook again (from the Start menu). If prompted, sign in and let it complete setup.
- If Outlook still will not open, repair or reinstall Office instead of just Outlook If the standalone Outlook uninstall fails, repairing or reinstalling the full Office suite typically resolves it.
- Use the Office repair/uninstall from Apps & Features (or Programs and Features) to remove Office 365/Office desktop apps.
- After uninstall completes, reinstall Office from the Microsoft 365 subscription portal or installation source.
- Open Outlook again and sign in/add accounts.
- If classic Outlook opens but behaves incorrectly, create a new Outlook profile A corrupted profile can prevent Outlook from starting or working correctly.
- Close Outlook.
- Open Control Panel.
- Select Mail > Show Profiles.
- Choose Add, give the profile a name, and select OK.
- Enter the primary email address and password and complete the setup wizard.
- Back in Show Profiles, select Prompt for a profile to be used (or set the new profile as default).
- Start Outlook and choose the new profile.
If Outlook works with the new profile, the old profile is corrupted and can be deleted later (after backing up any needed data files).
References:
- Troubleshoot Outlook for Windows issues
- Classic Outlook not responding, stuck at "Processing," stopped working, or freezes
- I can’t start Microsoft Outlook or receive the error “Cannot start Microsoft Outlook. Cannot open the Outlook Window”
- Detected a problem launching new Outlook - Microsoft Q&A
- What to do when Outlook will not open on my PC? - Microsoft Q&A
- How to fix the issue with MS Office asking you to log in every time you open an Office app - Microsoft Q&A