(Not Responding) message in title ribbon

Follow these steps in order until the issue is resolved.

1. Install the latest Windows and Office updates

• Outlook and other Office apps work best when fully updated.
• Install all recommended Windows and Office updates as described in Install Office updates.

2. Repair Office

• Close all Office apps (Outlook, Word, etc.).
• Open Control Panel → Programs and Features.
• In the list of installed programs, right-click Microsoft Office (Microsoft 365 Apps, Office 2016/2019/2021, etc.).
• Select Change → choose Repair (or Online Repair if available) and complete the repair.

3. Repair Outlook data files (if Outlook is frequently involved)

• Close Outlook.
• Run the Inbox Repair Tool (SCANSPST.EXE) and follow the steps in Repair Outlook Data Files (.pst and .ost) to scan and repair any errors.

4. Check for problematic add-ins (especially in Outlook)

• Close Outlook.
• Press Windows key + R, type:
  • Outlook /safe
  • Select OK.
• If Outlook runs without hanging, disable add-ins:
  • File → Options → Add-ins.
  • At the bottom, choose COM Add-ins → Go.
  • Clear all check boxes → OK.
  • Restart Outlook normally.
• Re-enable add-ins one by one, restarting Outlook each time, until the problem reappears. Remove the last add-in enabled if it causes the issue.

5. Update or adjust antivirus integration with Outlook

• If antivirus software integrates with Outlook, it can cause performance issues and “Not Responding” states.
• Disable Outlook-specific integration or Outlook add-ins provided by the antivirus product (from the antivirus settings or from Outlook Add-ins).
• Note: Changing antivirus settings can increase security risk; only adjust them if comfortable and consider consulting the antivirus vendor’s guidance.

6. Check for conflicting startup items or services (Selective Startup / Clean Boot)

• Open Control Panel → System and Security → Administrative Tools → System Configuration.
• On the General tab, select Selective startup.
• Clear Load system services and Load startup items.
• Then select Load system services only → OK → Restart.
• If the issue stops, use the Services and Startup tabs in System Configuration to enable items one by one (with restarts) to find the conflicting service or startup program.

7. Repair or reinstall Office if crashes persist across Word, Outlook, and other apps

• If repair does not help and all Office apps show “stopped working” or “not responding”, perform a full Online Repair from Apps/Programs and Features as above.
• If that still fails, completely uninstall Office, restart the PC, and reinstall Office from the Microsoft account or installation source.

8. Ensure device drivers (especially graphics) are up to date

• Some graphics drivers can cause Office apps to stop responding.
• Run Windows Update to install the latest drivers.
• If using an Intel graphics adapter, ensure the graphics driver is updated beyond any problematic versions listed in the documentation.

If, after these steps, Outlook or other Office apps still frequently show “(Not Responding)” and the screen clouds or whites out, collect details (which app, what action, any error messages) and contact Microsoft Support or post on Microsoft Q&A with those specifics for further investigation.

References:

• Outlook not responding error or Outlook freezes when you open a file or send mail
• Outlook not responding, stuck at "Processing," stopped working, or freezes
• Classic Outlook not responding, stuck at "Processing," stopped working, or freezes
• I get a "stopped working" error when I start Office applications on my PC
• Some Office applications are not responding
• Outlook crashes or stops responding when used with Office 365