Outlook won't open. Solutions for "Cannot start Microsoft Outlook" error.

Fix 1. Check if Outlook is already running

Before trying anything else, confirm that no Outlook processes are running in the background, preventing the app from starting anew.

1. Press Ctrl + Shift + Esc to open Task Manager. Or right-click the taskbar and select Task Manager.
2. Under Processes, look for Outlook items.
3. If you see any, right-click it and choose End task.
4. Try launching Outlook again.

If Outlook crashed silently earlier, this simple step often brings it back.

Fix 2: Start Outlook in Safe mode

Starting Outlook in safe mode actually means loading the app without any add-ins or custom settings. It's a quick way to check if a faulty plug-in or customization is interfering when Outlook tries to open.

To run Outlook in safe mode, click on its icon in the Start menu or Windows taskbar while holding the Ctrl key. In a pop-up window that appears, click Yes to confirm.

Another way is to use the following command in the Run dialog: outlook /safe. If prompted, select your default Outlook profile and click OK to open it.

If Outlook starts fine in safe mode, one of your add-ins is likely to be the problem. Try to disable the add-ins one at a time to detect which one is causing the issue.

Fix 3: Install latest Outlook updates

Outdated builds of Outlook can sometimes cause startup issues, especially if a recent patch addressed a bug that affects how the app loads. A quick update may be all you need to get Outlook working again without further troubleshooting.

For detailed information, see how to update Outlook.

Also, keep in mind that support for Office 2016 and Office 2019 clients connecting to Microsoft 365 services ended in 2023. Microsoft has stated that these versions won't be intentionally blocked, but they are no longer tested with new Microsoft 365 services. As a result, users may encounter unpredictable connection problems, reduced performance, or features that no longer work as expected.

Fix 4. Reset Navigation Pane configuration file

The Navigation pane (the left-hand panel where you access Mail, Calendar, People, and Tasks) relies on a small XML file that stores its settings. When this file becomes corrupted, Outlook may fail to start. A noticeable sign of corruption is when the file shows a size of 0 KB in its folder. No one knows the exact reason why this happens, but all versions of Outlook from 2010 to Microsoft 365 may be affected.

Resetting the file usually resolves the problem without affecting your mailbox data. Here's how to do it:

1. Press Win + R to open the Run dialog.
2. Type the following command: outlook.exe /resetnavpane
3. Press Enter or click OK.

This command resets the navigation pane settings for your default Outlook profile if you have more than one. If no default profile is set, Outlook is expected to prompt you to choose one before the reset takes place.

Delete Navigation pane file

If the reset command doesn't fix the issue, you can delete the XML file. Outlook will recreate it automatically the next time it starts.

1. Open the folder that contains the navigation pane file. For this, you can either:
   • Go to:
     C:\Users\<username>\AppData\Roaming\Microsoft\Outlook\profile_name.xml
   • Quickly access it by entering this path in File Explorer:
     %appdata%\Microsoft\Outlook
2. Locate the .xml file that has the same name as your Outlook profile and delete it.

Note.Try the reset command first. Deleting the XML file is the last resort if other options don't work.

Fix 5. Repair Outlook data file (.pst)

A damaged PST file is a frequent reason Outlook won't launch. Corruption can occur after an interrupted update, a system crash, or issues with your drive. When the data file can't be read properly, Outlook may stop at startup.

Microsoft provides a built-in tool called SCANPST.EXE that can diagnose and repair problems with .pst and .ost files. Follow the instructions in the Repairing Outlook Data Files guide, let the tool run a full scan, and complete the repair process. Once it's done, try opening Outlook again. If it launches normally, you are all set and do need the rest of the troubleshooting steps :)

Fix 6. Change the default Outlook account

If you have more than one account set up in Outlook, startup issues can occur when the program can't access the default PST file. The file itself may be perfectly fine, just temporarily unavailable. For example, when the file is stored on a network share or in a cloud folder like OneDrive that can't be reached at the moment. It can also happen if the PST file was moved or deleted. When Outlook can't locate the primary data file, it may refuse to open.

If this sounds like your situation, switching the default account (and consequently the default data file) can help. Here is how to do this without opening Outlook:

1. Go to Control Panel > Mail.
2. In the Mail Setup window, select Data Files… .
3. In the Account Settings window, choose another account that has a valid data file and click Set as Default.

Once the default account is changed, try starting Outlook again. If the original data file becomes available later, you can switch back at any time.

Fix 7. Repair Microsoft 365 or Office

If Outlook's program files are damaged or incomplete, repairing the installation usually resolves the issue. Here is a quick way to do this:

1. Navigate to Settings > Apps > Installed apps.
2. Find Microsoft Office or Microsoft 365 in the list.
3. Click the 3-dots to the right of the app and select Modify.
4. Pick Quick Repair first. Once the repair finishes, restart your computer and try opening Outlook again.
5. If Outlook still won't open, try Online Repair.

For more details, see How to repair Outlook 365 – 2013.

Fix 8. Create a new Outlook profile

If neither repairing the data file nor fixing the Microsoft 365 installation helps, the problem may lie in your Outlook profile.

Opening Outlook with a new profile can help you determine whether the original one is corrupted. The steps are:

1. Create a new profile. Go to Control Panel > Mail > Show Profiles > Add. Enter a name for the new profile and click OK.
2. Add a single account. Follow the prompts to add your email account. If possible, start with an Exchange-based account as it syncs with the server and usually avoids issues related to local Outlook data files.
3. Choose to be prompted for a profile. After the profile is created, enable Prompt for a profile to be used, then click OK.
4. Test Outlook. Launch Outlook with the new profile. If it opens normally, you can begin adding your other accounts.
5. Import data. If you have a POP3 account, you can try importing emails and other data from your old PST file.

For more information, see how to create a new Outlook profile.