OUTLOOK WILL NOT OPEN AS EXPECTED AND HAS BEEN WORKING UNTIL RECENTLY

Try these steps in order until Outlook opens normally:

1. Start Outlook in Safe Mode
   1. Close Outlook.
   2. Press Windows + R.
   3. Type Outlook /safe and select OK.
   4. If prompted, accept the default profile and sign in.
   • If Outlook does NOT start in safe mode, skip to step 3 (new profile). • If Outlook starts in safe mode, disable add-ins (step 2).
2. Disable all add-ins (if Outlook opens in Safe Mode)
   1. In Outlook, go to File > Options > Add-ins.
   2. At the bottom, ensure Manage: COM Add-ins is selected, then choose Go.
   3. Clear all check boxes to disable every add-in, then choose OK.
   4. Close Outlook (File > Exit).
   5. Start Outlook normally (without /safe).
   • If Outlook opens, re-enable add-ins one at a time (File > Options > Add-ins > Go) and restart Outlook after each to find the problematic add-in. Leave the bad add-in disabled.
3. Reset the Navigation Pane
   1. Close Outlook.
   2. Press Windows + R.
   3. Type Outlook.exe /resetnavpane and select OK.
   4. Try opening Outlook again.
4. Create a new Outlook profile A corrupted profile can prevent Outlook from opening.
   1. Follow the steps in Create an Outlook profile to create a new profile.
   2. Restart Outlook.
   3. In the Choose Profile dialog, select the new profile and choose OK.
   • If Outlook opens with the new profile, the old profile is corrupted. Use the new one going forward. If removing the old profile later, back up data files first because cached offline content will be deleted.
5. Repair Outlook data files If Outlook still will not open, the data file may be corrupted.
   1. Close Outlook.
   2. Run the Inbox Repair Tool (scanpst.exe) as described in Repair Outlook Data Files (.pst and .ost).
   3. After repair completes, try opening Outlook again.
6. If Outlook closes shortly after opening If Outlook briefly opens then stops responding and closes, and the Windows Event Viewer shows events matching the issue described in the context, sign out of Office and sign back in to repopulate identity settings. If needed, follow the registry-based workarounds in the article "Outlook closes shortly after it is opened" or update to a fixed build if applicable.
7. If none of the above works If Outlook still will not open after safe mode, disabling add-ins, resetting the navigation pane, creating a new profile, and repairing data files, perform an Office repair as described in Repair an Office application. If that fails, uninstall Office 365/Microsoft 365 and reinstall from the subscription, as this has resolved similar cases.

References:

• I can’t start Microsoft Outlook or receive the error “Cannot start Microsoft Outlook. Cannot open the Outlook Window”
• Outlook for Windows not responding, hangs, freezes, or stops working
• Outlook closes shortly after it is opened
• What if Outlook can not open after the failure of transferring Outlook related files?
• Outlook suddenedly will not open on my PC?