Fixes / Outlook · Checked

Outlook "Cannot open the Outlook window": causes and fixes

Short answer

This error comes from classic Outlook for Windows. It means Outlook began starting but could not build its main window. The usual cause is a corrupted navigation pane settings file. Close Outlook, press Windows key + R, type Outlook.exe /resetnavpane and press Enter. If that doesn't work, start it with Outlook /safe to check for a bad add-in, then create a new profile.

What this message means

Classic Outlook (Microsoft 365, 2024, 2021, 2019, 2016) loads several things before it shows its main window: your mail profile, the data file (.pst or .ost), the navigation pane layout and any add-ins. If one of them fails to load, Outlook stops and shows this message instead of opening. Your email is almost always still safe. With Microsoft 365 and Exchange accounts it is stored on the server, and a local .pst file is usually only damaged, not lost. The new Outlook for Windows and Outlook for Mac don't show this message. If you see a similar error there, it has a different cause.

Common causes

CauseHow to tell
Corrupted navigation pane settings file (profilename.xml)Outlook fails immediately every time, often right after a crash or a forced shutdown. The file %appdata%\Microsoft\Outlook\<profile name>.xml may show as 0 KB. The /resetnavpane fix solves it at once.
A faulty or outdated add-inOutlook opens normally with Outlook /safe ("Safe Mode" appears in the title bar) but fails when started normally. It often starts after installing or updating software that adds an Outlook plug-in, such as PDF, CRM, antivirus or ABBYY FineReader add-ins.
Corrupted Outlook profileSafe mode also fails with the same message, but a newly created profile opens without problems.
Damaged .pst or .ost data fileThe error appears together with "The set of folders cannot be opened", or Outlook stops at "Loading profile". It often follows a crash, a full disk or a data file stored on a network or USB drive.
Outlook still running in the background, or started in compatibility modeTask Manager shows Microsoft Outlook (OUTLOOK.EXE) running even though no window is open. Or the Compatibility tab in OUTLOOK.EXE's Properties has "Run this program in compatibility mode for" ticked.
Microsoft 365 or Exchange sign-in problem on the server sideThe message adds "The attempt to log on to Microsoft Exchange has failed", several users in the same organization see it at once, and Outlook on the web (outlook.office.com) still works.

How to fix it

1. Close hidden Outlook processes and restart

  1. Press Ctrl + Shift + Esc to open Task Manager.
  2. On the Processes tab, look for Microsoft Outlook, and on the Details tab for OUTLOOK.EXE.
  3. Select each one and click End task.
  4. Restart the computer if Outlook was stuck, then open Outlook again.

2. Reset the navigation pane

Classic Outlook for Windows (Microsoft 365, 2024, 2021, 2019, 2016), Windows 10 and 11

  1. Make sure Outlook is fully closed (see the fix above).
  2. Press Windows key + R to open the Run box.
  3. Type Outlook.exe /resetnavpane and click OK.
  4. Outlook should open with the default folder pane. Any custom folder order or Favorites in the pane are reset, but no mail is deleted.

3. Start in safe mode and turn off add-ins

Classic Outlook for Windows

  1. Press Windows key + R, type Outlook /safe and click OK. (Holding Ctrl while clicking the Outlook icon also works.)
  2. Accept the default profile in Choose Profiles and click OK.
  3. If Outlook opens, go to File > Options > Add-ins. Set Manage to COM Add-ins and click Go.
  4. Take a screenshot of the list, clear every checkbox (don't click Remove) and click OK.
  5. Close Outlook with File > Exit and open it normally.
  6. If it now works, turn the add-ins back on one at a time until the error comes back. The last one you turned on is the problem, so update or remove it.

4. Create a new Outlook profile

Classic Outlook for Windows. On Windows 11, open Control Panel by searching for "Control Panel" in Start.

  1. Close Outlook. Open Control Panel, set View by to Large icons and open Mail (Microsoft Outlook). You can also press Windows key + R and run Outlook.exe /profiles.
  2. Click Show Profiles, then Add. Give the profile a new name and click OK.
  3. Enter your email address and password and finish the account setup.
  4. Under "When starting Microsoft Outlook, use this profile", select Always use this profile, choose the new profile and click OK.
  5. Open Outlook. If it works, the old profile was corrupted. Once you have checked that your mail is all there, you can remove the old profile.

5. Repair or rebuild the data file

Classic Outlook for Windows. On Microsoft 365, 2019 and 2016 Click-to-Run, SCANPST.EXE is usually in C:\Program Files\Microsoft Office\root\Office16 (64-bit) or C:\Program Files (x86)\Microsoft Office\root\Office16 (32-bit).

  1. Close Outlook completely.
  2. For a .pst file (POP, IMAP or archive): open SCANPST.EXE from the Office16 folder, click Browse and select your .pst file (usually in Documents\Outlook Files).
  3. Click Start. If it reports errors, keep "Make backup of scanned file before repairing" ticked and click Repair.
  4. For Microsoft 365, Exchange or Outlook.com accounts (.ost file): open %localappdata%\Microsoft\Outlook in File Explorer and rename the .ost file to .old. Outlook downloads a fresh copy from the server when it next starts.
  5. Open Outlook again. A large mailbox may take a while to sync.

6. Turn off compatibility mode and repair Office

Windows 10 and 11. Online Repair needs an internet connection.

  1. Right-click the Outlook shortcut, choose Open file location, then right-click OUTLOOK.EXE and choose Properties > Compatibility.
  2. Clear "Run this program in compatibility mode for" and click OK.
  3. If Outlook still fails, open Settings > Apps > Installed apps (Windows 11) or Settings > Apps > Apps & features (Windows 10).
  4. Find Microsoft 365 or Microsoft Office, then choose Modify (on Windows 11 it's under the three-dot menu).
  5. Choose Quick Repair first. If that doesn't fix it, run Online Repair, then restart the computer.

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Still not fixed?

If none of the fixes work, sign in at outlook.office.com (work or school, Microsoft 365) or outlook.com (personal accounts) to check that your mail and account are fine. You can keep working there, or in the new Outlook for Windows, while you troubleshoot. If the message mentions Microsoft Exchange, or several colleagues see it at the same time, the problem is probably on the server side. Your IT admin can open a support case in the Microsoft 365 admin center. Home users can run the Microsoft Support and Recovery Assistant or contact Microsoft Support through the Get Help app.

Questions people ask

Will I lose my emails if I reset the navigation pane or create a new profile?

No. /resetnavpane only resets the folder pane layout. A new profile connects to the same mailbox. With Microsoft 365, Exchange and IMAP accounts the mail is stored on the server, and a .pst file stays on disk until you delete it.

What does Outlook.exe /resetnavpane do?

It deletes and rebuilds the XML file that stores your folder pane settings, such as Favorites and shortcuts. It's the most common single fix for this particular message.

Why does Outlook open in safe mode but not normally?

Safe mode loads Outlook without add-ins, so an add-in is almost certainly failing at startup. Turn them off under File > Options > Add-ins > COM Add-ins > Go, then turn them back on one at a time to find the faulty one.

Is it safe to delete the .ost file?

Yes, if the account is Microsoft 365, Exchange or Outlook.com. The .ost file is only a local copy, and Outlook downloads it again from the server. Don't delete a .pst file, because that may be the only copy of the mail. Repair it with SCANPST.EXE instead.

Does this error happen in the new Outlook or on Mac?

No. This exact message is only shown by classic Outlook for Windows. The new Outlook for Windows and Outlook for Mac use different startup code and show different errors.

Sources

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