KB Article – Outlook Cannot Start / Cannot Open the Outlook Window

Outlook Cannot Start / Cannot Open the Outlook Window

Document ID: KB-OUT-016-START
Version: 1.0
Date: 27/08/2025
Author: Ante Crvelin
Audience: IT Infrastructure, Service Desk, End Users
Scope: Applies to Microsoft Outlook 2010, 2013, and 2016 (Makita AU).

1. Overview & Purpose

Users may receive an error where Outlook fails to start and displays “Cannot start Microsoft Outlook. Cannot open the Outlook window.”

This KB provides troubleshooting steps to resolve the issue, focusing on Safe Mode, disabling add-ins, repairing data files, and checking compatibility settings.

2. Symptoms

Outlook does not launch.
Error message: “Cannot start Microsoft Outlook. Cannot open the Outlook window.”
Outlook hangs on startup.

3. Causes

Corrupt add-ins are preventing Outlook from loading.
Corrupt Outlook data files (.pst / .ost).
Outlook running in Compatibility Mode (Outlook 2010/2013 only).

4. Procedure

Step 1 – Start Outlook in Safe Mode

Press Start > Run.
Type:
```
outlook /safe
```
Select the default Outlook profile and click OK.
- If prompted, enter your password.
Verify that Outlook launches in Safe Mode (the label is displayed in the title bar or taskbar icon).

👉 If Outlook opens in Safe Mode, the issue is likely related to add-ins. Proceed to Step 2.

Step 2 – Disable Add-ins

In Outlook, go to File > Options > Add-ins.
At the bottom, in the Manage box, select COM Add-ins, then click Go.
Record the list of enabled add-ins (screenshot or notes).
Clear all checkboxes to disable them, then click OK.
Restart Outlook normally.

👉 If Outlook loads successfully, re-enable add-ins one at a time until the problematic add-in is found.

Step 3 – Repair Outlook Data Files

Close Outlook.
Locate and run the Inbox Repair Tool (scanpst.exe).
- Location depends on Outlook version:
  - Outlook 2013 → C:\Program Files\Microsoft Office\Office15\
  - Outlook 2010 → C:\Program Files\Microsoft Office\Office14\
Scan and repair the Outlook data file.
Restart Outlook.

Step 4 – Check Compatibility Mode (Outlook 2010/2013 only)

Locate Outlook.exe:
- Outlook 2013 → C:\Program Files\Microsoft Office\Office15\
- Outlook 2010 → C:\Program Files\Microsoft Office\Office14\
Right-click Outlook.exe → Properties → Compatibility tab.
Ensure no boxes are checked.
Click Apply > OK.
Restart Outlook.

5. Validation / Testing

Confirm Outlook launches successfully without errors.
Verify that the user can access the mailbox and open the Outlook window.
If Safe Mode was required, re-enable add-ins one at a time until stable.

6. Troubleshooting

If Outlook still fails to start:
- Check Windows Event Viewer for Application errors related to Outlook.
- Create a new Outlook profile via Control Panel > Mail > Profiles.
- Test Outlook Web Access to confirm account functionality.

7. Risks / Considerations

Disabling add-ins may remove features users rely on (e.g., CRM integrations, third-party plugins).
Repairing PST/OST files may take time for large files.
Compatibility Mode only applies to Outlook 2010/2013, not 2016.