Windows 10 Installed Outlook won't start, but can read email in browser

If you use Outlook on a Windows computer and Outlook doesn't open or opens with problems, try these troubleshooting steps in the order presented here, from simple to more complicated.

If you use the cloud-based Microsoft 365 on a PC or a Mac, the automated Support and Recovery Assistant tool can diagnose and fix many issues, including the problem of Microsoft Outlook not starting.

Open Outlook in Safe Mode. If Outlook opens as expected in Safe Mode, the issue is likely an add-in or toolbar extension.

Disable add-ins. One or more add-ins could be conflicting with Outlook and cause the problem. Disable all add-ins and see if this resolves the issue.

Select File > Options > Add-ins.
In the Manage section, select Go.
Clear the check boxes next to the add-ins you want to disable.
Select OK.
Scan your system for viruses, Trojans, spyware, and other malware. If you find a problem, resolve it with your security software, reboot your computer and try restarting Outlook again.

How to Properly Scan Your Computer for Viruses
Repair Outlook. The Outlook application may be damaged. Use the built-in Microsoft Office repair utility to fix it.

Close all Office applications.
Go to Start > Control Panel.
Select Category View.
In the Programs section, select Uninstall a Program.
Right-click Microsoft Office and choose Change.
Select Online Repair or Repair. Choose Yes if a user account control prompt appears.
Restart Outlook after the process completes.
Repair your Outlook profile. Outlook profiles can become corrupted, causing all sorts of problems, including Outlook not opening.

Select File > Account Settings > Account Settings.
Go to the Email tab.
Choose Repair to open the Repair wizard (this option is not available for Outlook Exchange accounts).
Follow the prompts to complete the wizard and restart Outlook.
Repair Outlook data files. If Outlook still doesn't open, use the Inbox Repair tool to find and possibly fix the problem.

Exit Outlook.
Download and open the Inbox Repair tool from Microsoft.
Select Browse and navigate to your personal folders (.pst) file, then select Start.
Choose Repair if the scan finds errors.
When the repair is complete, restart Outlook.
Reset the navigation pane. A startup issue with the navigation pane can prevent Outlook from opening correctly. Resetting the navigation pane might resolve the issue.

Exit Outlook.
Go to Start > Run or press Windows Key+R.
Type or paste outlook.exe /resetnavpane and select OK.
Open Outlook. The navigation pane will be reset.