outlook classic doesn't start in Windows 10

Question

When I click Outlook, it seems that opens but suddenly disappears and dont start. I tried opening as administrator, changing profile, opening in safe mode but nothing works. I was able to open it once but when I closed it it opened anymore

Answer 1

Hi Rodrigo, 

I’m sorry you’re going through this issue, and I appreciate you sharing the troubleshooting steps you’ve already tried.

As a forum moderator, I genuinely wish I could directly access your account or review the backend systems to diagnose and resolve this issue for you. However, our role here is limited to providing general guidance by offering clear next steps, sharing applicable resources, and directing you to the appropriate support channels so you can work with the right team to investigate further. 

Since you have already tried opening Outlook as administrator, changing the Outlook profile, and starting Outlook in Safe Mode, this may not be a simple profile or add-in issue. 

This behavior can sometimes happen if there is a problem with the Outlook/Office installation, corrupted mailbox rules, a damaged Outlook cache/data file, or an issue with the current Outlook build.

As you haven’t specified your account type (work/school vs. personal), I may not be able to provide an exact solution yet. Assuming you’re using a work account, please try the steps below. If you’re using a personal account, please let me know and I’ll tailor the guidance for that scenario.  

1/ Run an Office Online Repair 

• Open Settings > Apps > Installed apps 
• Find Microsoft 365 / Microsoft Office 
• Select Modify 
• Choose Online Repair 
• Restart the computer after the repair completes, then try opening Classic Outlook again. 

2/ Try clearing Outlook rules 

If corrupted mailbox rules are causing Outlook to crash, clearing the rules may help. Please note that this may remove existing Outlook rules. 

• Close Outlook completely 
• Press Windows + R 
• Run:  outlook.exe /cleanrules 
• 
• Then try opening Classic Outlook again. 

3/ Rebuild the Outlook cache file 

If you are using a Microsoft 365 or Exchange account, Outlook may be loading a corrupted local cache file. Try rebuilding the OST file: 

• Close Outlook 
• Press Windows + R and go to:  %localappdata%\Microsoft\Outlook 
• Locate the related .ost file 
• Rename it, for example:  outlook_old.ost 
• Reopen Outlook and allow it to rebuild the mailbox cache. 

You may also refer to: Classic Outlook unexpectedly closes at start up on faulting module ucrtbase.dll | Microsoft Support 

4/ Reinstall Classic Outlook 

• As a final step, please uninstall Microsoft 365/Office from Settings > Apps > Installed apps, restart the device, then reinstall it from office.com or your organization’s approved installation source. 
• This can help replace any damaged Outlook or Office components
• Reference: Download, install, or reinstall Microsoft 365 or Office 2024 on a PC or Mac | Microsoft Support

If the issue still continues after trying the steps above, please reach out to your organization’s IT department. They can help further investigate the device, Office installation, mailbox configuration, event logs, and any organization-managed policies or add-ins that may be affecting Classic Outlook.

Additionally, if needed, your IT team can also raise a support ticket with Microsoft Support through the Microsoft 365 Admin Center for deeper investigation. They have access to backend configurations and can perform a more in-depth investigation. At the very least, they can provide the most effective workaround to ensure your experience remains smooth and secure.      

In case you do not know who is your IT admin, kindly refer to this article: How do I find my Microsoft 365 admin? - Microsoft Support  

I hope this information is helpful. Should you have any further questions or need additional assistance, please feel free to share them in the comment below. I'm very happy to help.  

I'm looking forward to hearing your thoughts. 

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Answer 2

Hi Rodrigo,

Since safe mode and profile changes didn't work, Outlook is likely stuck running as a ghost process or has a corrupted installation. Try these steps:

End Task in Task Manager:

Press Ctrl + Shift + Esc. Look for Microsoft Outlook under the Processes tab. If it's there, right-click it and select END Task. then try reopening it.

Run an Office Repair:

Open Windows Settings > Apps > Apps & Features Find your Microsoft Office / 365 installation, click Modify, and choose Quick Repair.

Disable Add-ins via Registry (If Safe Mode fails to open):

Press Win + R, type regedit, and navigate to HKEY_CURRENT_USER\Software\Microsoft\Office\Outlook\Addins. Rename the folder to Addins.old to force Outlook to launch without any third-party interference.