How to Fix “Cannot Start Microsoft Office Outlook. Cannot Open the Outlook Window.” in Windows 10 and 11 (2026)

“Cannot start Microsoft Office Outlook. Cannot open the Outlook window.” This error blocks Outlook from launching entirely, and it hits classic Outlook for Windows most often after a profile corruption, a bad add-in, or a recent Office update.

This guide covers classic Outlook for Windows in Microsoft 365, Office 2021, Office 2019, and older versions on Windows 10 and 11. Steps are the same unless noted.

Fix #1: Reset the Navigation Pane

A corrupted navigation pane cache (profilename.xml) is the single most common cause of this exact error. Resetting it takes ten seconds and fixes the problem for most people.

1. Close Outlook completely.
2. Press Windows + R to open the Run dialog.
3. Type outlook.exe /resetnavpane and press Enter.

Outlook should open normally. If it does, you’re done. If the error returns, move to Fix #2.

Fix #2: Start Outlook in Safe Mode and Disable Add-ins

A faulty COM add-in, often from antivirus software, PDF tools, or CRM integrations, can prevent the Outlook window from rendering at all. Safe Mode bypasses add-ins so you can identify the culprit.

1. Press Windows + R.
2. Type outlook.exe /safe and press Enter.

If Outlook opens in Safe Mode, an add-in is causing the crash. Disable them all, then re-enable one at a time:

3. In Outlook, go to File > Options > Add-ins.
4. At the bottom of the screen, set Manage to COM Add-ins and click Go…
5. Uncheck every add-in and click OK.
6. Close Outlook and reopen it normally (without /safe).
7. If Outlook opens, re-enable add-ins one at a time, restarting Outlook after each, until you find the one that triggers the error.

Fix #3: Repair or Recreate Your Outlook Profile

Profile corruption is the second most common cause. You can try repairing the existing profile first, then create a fresh one if repair doesn’t help.

1. Close Outlook.
2. Open Control Panel. In Windows 10/11, press Windows + R, type control, and press Enter. Set View by to Small icons.
3. Click Mail (Microsoft Outlook).
4. Click Show Profiles…

5. Select your existing profile and click Properties, then Email Accounts… to check for obvious account errors. If the profile looks intact, skip to step 6.
6. To create a new profile, click Add…, give it a name, and add your email account. For Microsoft 365 accounts, Autodiscover will rebuild your mailbox automatically once you sign in.
7. Select Always use this profile, choose the new profile from the dropdown, and click OK.
8. Open Outlook and sign in when prompted.

Note: If you store email locally in a PST file (not Exchange or Microsoft 365), back up the PST before deleting your old profile. PST files are typically found at C:\Users\[YourName]\Documents\Outlook Files\. Exchange Online and IMAP mailboxes will resync automatically from the server.

Fix #4: Scan and Repair Your PST File with ScanPST

If your local data file (.pst or .ost) is corrupted, Outlook may fail to open even with a healthy profile. Microsoft’s built-in Inbox Repair Tool (ScanPST.exe) can fix this.

1. Close Outlook.
2. Open File Explorer and navigate to the ScanPST location for your Office version:
   • Microsoft 365 / Office 2019 / 2021 (64-bit): C:\Program Files\Microsoft Office\root\Office16\
   • Microsoft 365 / Office 2019 / 2021 (32-bit): C:\Program Files (x86)\Microsoft Office\root\Office16\
3. Double-click SCANPST.EXE.
4. Click Browse and navigate to your PST or OST file. The default location is C:\Users\[YourName]\AppData\Local\Microsoft\Outlook\.
5. Click Start. If errors are found, click Repair.

Once the repair completes, reopen Outlook normally.

Fix #5: Check Microsoft 365 Service Health

If Outlook was working fine and suddenly stopped, especially if colleagues are affected too, the problem may be a Microsoft 365 service outage rather than anything on your machine.

1. Open a browser and go to Downdetector for Outlook to check for widespread reports.
2. If you’re an admin or have access to the Microsoft 365 admin center, check Health > Service health for active incidents.
3. If an outage is confirmed, use Outlook on the web as a temporary workaround while Microsoft resolves the issue.

There’s nothing to fix locally during a service outage. Waiting it out, or using webmail, is the right call.

Fix #6: Repair Microsoft 365 or Office

A broken or incomplete Office installation can cause startup failures that none of the above steps will touch. Run a Quick Repair first; if that doesn’t work, run Online Repair.

1. Close all Office applications.
2. Right-click the Start button and select Installed apps (Windows 11) or Apps and Features (Windows 10).
3. Find Microsoft 365 or Microsoft Office 2019/2021 in the list.
4. Click the three-dot menu (Windows 11) or select the entry (Windows 10), then click Modify.
5. Select Quick Repair and click Repair. Wait for it to finish, then try Outlook.
6. If the error persists, repeat steps 2–4 and choose Online Repair instead. This downloads fresh Office files and performs a deeper reset, so it takes longer but is more thorough.

7. Restart your PC and open Outlook.

Fix #7: Run Microsoft Support and Recovery Assistant (SaRA)

Microsoft’s Support and Recovery Assistant (SaRA) is a free diagnostic tool that automatically detects and fixes many Outlook startup, profile, and connectivity problems, including this exact error.

1. Download SaRA from Microsoft’s official SaRA page.
2. Run the installer and open the tool.
3. Select Outlook from the product list, then choose Outlook won’t start.
4. Follow the on-screen prompts. SaRA will run diagnostics and either fix the problem automatically or tell you exactly what’s wrong.

SaRA is particularly useful if you’ve worked through Fixes #1–6 without success, or if you’re in a business environment with Exchange Online where server-side issues might be contributing.

Bonus: Disable Hardware Graphics Acceleration

On some Windows 10/11 machines, display driver or DPI scaling issues prevent the Outlook window from rendering, producing the same startup error. This is less common but worth trying if nothing else has worked.

1. Open Outlook in Safe Mode: press Windows + R, type outlook.exe /safe, press Enter.
2. Go to File > Options > Advanced.
3. Under the Display section, check Disable hardware graphics acceleration.
4. Click OK, close Safe Mode, and reopen Outlook normally.

When the Fixes Don’t Work

If you’ve worked through every fix above and Outlook still won’t open, the last resort is a full uninstall and reinstall of Microsoft 365 or Office. Uninstall via Installed apps, reboot, then reinstall from your Microsoft account or installation media. Before you do, make sure any local PST files are backed up. Exchange Online and IMAP mail will resync automatically, but local-only data won’t. If you’re in a business environment, loop in your IT admin at this point, as the issue may be server-side or related to account licensing.

Conclusion

Resetting the navigation pane (Fix #1) or disabling add-ins (Fix #2) resolves this error for the vast majority of people, so try those first before anything else. If the error keeps coming back after a fix, profile corruption is usually the deeper cause, and creating a fresh profile (Fix #3) will clear it permanently. Recurring failures after Office updates are worth checking against Microsoft’s known issues page for classic Outlook, where Microsoft tracks and documents update-specific bugs.