Outlook won't open

Start Outlook Classic in Safe Mode first; if it opens, disable its COM add-ins because one of them is preventing normal startup.

1. Test Outlook in Safe Mode

1. If Outlook remains on the splash screen, press Ctrl + Shift + Esc.
2. In Task Manager, select Microsoft Outlook and choose End task.
3. Press Windows key + R.
4. Enter:

Outlook.exe /safe

5. Select OK, accept the default profile, and enter your password if prompted.

Safe Mode starts Outlook without COM add-ins. If Outlook opens successfully, continue with the next section. ^1^

2. If Safe Mode works, isolate the faulty add-in

While Outlook is open in Safe Mode:

1. Select File → Options → Add-ins.
2. At the bottom, set Manage to COM Add-ins, then select Go.
3. Take a screenshot or note which add-ins are enabled.
4. Clear every checkbox and select OK. Disable the add-ins; do not select Remove.
5. Exit Outlook and open it normally.
6. If it now opens, enable the add-ins one at a time, restarting Outlook after each one. Leave the add-in that causes the hang disabled. ^1^

3. If Safe Mode also hangs

Try these in order.

Reset the navigation pane

This removes navigation-pane customizations but does not delete email:

1. Close Outlook and end any remaining Outlook process in Task Manager.
2. Press Windows key + R.
3. Enter:

Outlook.exe /resetnavpane

4. Select OK and check whether Outlook opens. ^1^

Test a new Outlook profile

1. Open Control Panel.
2. Search for and open Mail (Microsoft Outlook).
3. Select Show Profiles → Add.
4. Create a profile and add your email account.
5. Hold Shift while starting Outlook.
6. Select the new profile and choose OK.

If Outlook opens with the new profile, the original profile is damaged. Do not remove the old profile until any locally stored data has been backed up; removing a profile deletes its offline cached content. ^1^

Repair Microsoft 365

1. Open Settings → Apps → Installed apps.
2. Find Microsoft 365 or Office.
3. Select its menu, then Modify.
4. Run Quick Repair.
5. If Outlook still hangs, repeat the process and run Online Repair. Online Repair is the more extensive option. ^2^

Classic Outlook startup troubleshooters are also available through the Windows Get Help app. They apply to Classic Outlook, not new Outlook for Windows. ^3^

References

1. I can’t start Microsoft Outlook or receive the error “Cannot start Microsoft Outlook. Cannot open the Outlook Window” | Microsoft Support
2. Classic Outlook(#tab/classic-outlook)
3. Resolve Outlook for Windows issues with automated troubleshooting tools | Microsoft Support