Excel and Outlook Not Responding? Causes and Fixes

If Excel and Outlook both show Not Responding, restart Windows, install pending Microsoft 365 updates, and test the apps without add-ins; a shared Office component, add-in, or Windows issue may be affecting both. If only one file or mailbox view freezes, investigate that item separately before closing the app, because unsaved work may be lost.

What Not Responding means

Not Responding is a Windows status, not a diagnosis. It means an app has stopped replying to Windows for a time. Excel or Outlook may be busy calculating, refreshing data, loading a large mailbox, or waiting for a network resource; the same message can also appear when the program has genuinely become stuck. A pause alone does not prove that a file is damaged.

If the pointer shows a busy indicator or the window becomes responsive again after a minute, let the task finish. Large Excel workbooks with many formulas, data connections, or pivot tables can take time to recalculate. Outlook can pause while syncing a mailbox or opening a large attachment. Repeatedly clicking the window, launching more copies, or ending the process immediately can make it harder to tell whether work is still being saved.

When both programs freeze around the same time, consider shared causes first: a recent Office update, an add-in used by one or both apps, low available memory, a security or synchronization tool, or a problem with the Office installation. When one workbook or one mailbox action consistently triggers the freeze, the cause may instead be specific to that content or task.

Start with low-risk checks

Before changing settings, note what was happening when the freeze began. Was Excel opening a particular workbook, refreshing a connection, or running a macro? Was Outlook synchronizing, searching, sending, or opening an attachment? This detail helps separate a general app problem from a repeatable trigger.

Wait briefly if the app may be processing a large task. Check whether disk or network activity is ongoing rather than clicking repeatedly.
Save any other open work in responsive apps. If the frozen app recovers, save its file under a new name before continuing diagnosis.
Press Ctrl+Shift+Esc to open Task Manager. On Windows, check whether Excel or Outlook is using substantial CPU or memory, but do not assume that high usage alone means a failure.
If an app remains frozen, select it in Task Manager and choose End task only when you accept that unsaved changes in that app may be lost. Reopen it once; avoid repeatedly killing and relaunching it.
Restart Windows if several Office apps are affected, then try the apps before reopening every workbook, browser tab, or background utility.

Excel may offer Document Recovery after an unexpected close, but it is not guaranteed to restore every recent change. Outlook normally stores mail on the server for many Microsoft 365 and Exchange accounts, but unsent messages, local-only folders, and unsaved drafts can still be at risk. Do not treat force-closing an app as a way to safely preserve work.

Test Excel and Outlook in Safe Mode

Safe Mode is a useful isolation test in the classic Windows desktop versions of Excel and Outlook. It starts Excel with restricted startup behavior and starts classic Outlook without its usual add-ins and some customizations. It does not repair files or remove add-ins. If an app works in Safe Mode but freezes during a normal launch, an add-in or startup customization is a strong suspect.

Close the app if possible. Press Windows key+R to open the Run dialog.
To test Excel, enter excel /safe and press Enter. To test classic Outlook, enter outlook.exe /safe and press Enter.
Try the action that usually causes the freeze, using a copy of the workbook where practical. If it works, close the app and continue by checking add-ins.
If the same freeze happens in Safe Mode, look beyond add-ins: test another file or Outlook action, install updates, and consider Office repair.

These commands are for classic desktop Outlook on Windows. They do not provide the same Safe Mode test for the newer Outlook for Windows app; its interface and support for add-ins differ. On a Mac, Windows Run commands do not apply. Update Office through Microsoft AutoUpdate, check available add-ins in the relevant app settings, and restart the Mac before testing again. Menu labels can vary with the Outlook version.

Disable add-ins methodically

Add-ins can extend Office with PDF tools, meeting integrations, data connectors, antivirus features, or custom business functions. A faulty or incompatible add-in may slow startup or cause a freeze, sometimes after an Office update. Do not remove every add-in at once: disabling them in a controlled way makes it easier to identify the one associated with the problem.

In Excel for Microsoft 365 on Windows, open File > Options > Add-ins. At the bottom, use the Manage list to select COM Add-ins, then choose Go. Clear the check box for an add-in and restart Excel. You can also inspect Excel Add-ins from the Manage list. Record which items you disable so you can restore them if they are unrelated.

In classic Outlook for Windows, use File > Options > Add-ins, choose COM Add-ins in the Manage list, and select Go. Disable one item, restart Outlook, and repeat the action that caused the hang. If the problem disappears, check with the add-in publisher or your organization’s IT team for a compatible version before permanently removing a business-required tool. The newer Outlook app does not use classic Outlook COM add-ins; it uses a different add-in model.

Check the workbook or Outlook task

If Excel freezes only with one workbook, make a copy before troubleshooting. Open a different workbook to see whether the issue is limited to that file. A workbook can be slow because it contains extensive formulas, volatile calculations, external links, large data models, or connections to a network or cloud source. Refreshing a connection may wait on a remote service even while Excel itself is operating normally.

For a workbook that opens, test a copy with automatic calculation temporarily set to manual from Formulas > Calculation Options > Manual. This can help identify whether repeated recalculation is responsible; it is not a general fix, and formulas will not recalculate automatically until calculation is restored or initiated. Be especially careful with business-critical models, since displayed results may be out of date while calculation is manual. If a macro or external connection triggers the freeze, investigate that specific process rather than assuming Office is broken.

If Outlook freezes during one operation, compare it with another: for example, open a different message, try a search in a smaller folder, or test sending a brief message to yourself if company policy permits. A large attachment, a shared mailbox, a slow connection, or a mailbox synchronization backlog may explain a delay. If Outlook is stuck on sending, check the Outbox and connection status before sending the message again, so you do not accidentally create duplicates.

Install updates and repair Microsoft 365

Office updates can include reliability fixes, while a Windows restart can complete updates that are waiting to finish. In an Office desktop app on Windows, choose File > Account > Update Options > Update Now. If Update Options is unavailable, your organization may manage updates or the installation method may differ; ask IT rather than trying to bypass company controls. On Mac, use Microsoft AutoUpdate to check for Office updates.

If the apps still freeze, repair Microsoft 365 from Windows. Open Settings > Apps > Installed apps, find Microsoft 365 or Office, select its more-options menu, and choose Modify. Depending on the installation, Windows may offer Quick Repair and Online Repair. Quick Repair is the less extensive first option. Online Repair is more comprehensive and may require internet access and a fresh sign-in afterward. Save work and close Office apps before starting either repair.

Repair is different from deleting an Outlook profile or removing a workbook. It targets the Office installation, but it cannot guarantee recovery of unsaved work or fix a damaged individual file. If the repair options are missing, the device is managed, or the problem persists afterward, contact your organization’s support team or Microsoft support with the error details and the steps already tried.

Outlook profiles, data files, and account differences

If Excel is stable and Outlook alone keeps freezing, an Outlook profile or local mail data may be involved. For classic Outlook, a new profile can be tested using the Windows Control Panel’s Mail (Microsoft Outlook) option, then Show Profiles. The exact Control Panel label may vary. Add the account to a separate profile for testing rather than deleting the existing one. If the new profile works, that points toward a profile-specific configuration issue, though it does not by itself identify the cause.

Do not delete Outlook data files simply because Outlook is slow. An OST file is generally a local cached copy for supported account types and may be rebuilt, but the process and consequences depend on the account and configuration. A PST can contain locally stored mail or other data that is not safely replaceable by a server copy. Back up important local data and consult IT before removing or rebuilding files, especially on a work device or where retention requirements apply.

The newer Outlook for Windows and classic Outlook have different settings, add-in support, and troubleshooting paths. Confirm which app you are using before following instructions for profiles or COM add-ins. If the problem began after switching Outlook versions, mention that change when asking for help.

When to seek help and what to report

Contact IT or support if both apps continue to fail after restart, updates, and a Safe Mode check; if the issue affects several users; or if you see repeated crashes, Office sign-in errors, or a warning about a damaged file. Stop experimenting with local mail data when messages may exist only on the computer. On a managed device, IT may also need to check policies, security software, network access, or a centrally deployed add-in.

Useful details include the Windows version, Office update channel or build if available, whether you use classic or new Outlook, the exact error text, and whether the failure occurs in Safe Mode. Note whether all workbooks are affected or only one, and whether the problem began after an update or add-in installation. This information is more actionable than saying only that Office is slow.

Frequently Asked Questions

Why are Excel and Outlook both not responding?
They may share a cause such as an Office installation problem, a Windows resource shortage, an add-in, or a pending update. If only one file or one Outlook task triggers the freeze, the cause may instead be specific to that content or operation.

How do I force close Excel or Outlook?
Press Ctrl+Shift+Esc, select the frozen app in Task Manager, and choose End task. Unsaved changes may be lost, so wait briefly first if the app could be processing a large task.

Does Safe Mode delete my Excel files or Outlook mail?
No. Safe Mode changes how the app starts; it is a troubleshooting test, not a file deletion step. Still, save a workbook copy before testing if you can, and do not remove Outlook data files as part of a Safe Mode check.

What if Outlook freezes only when sending email?
Check whether the message is in the Outbox and whether Outlook is online before trying again. A large attachment, connection problem, or synchronization delay can hold up sending. Avoid repeated clicks that could send duplicates.

Will repairing Microsoft 365 erase my documents?
Office repair targets the installed applications, not the contents of your workbook folders. However, no repair process can protect unsaved changes or substitute for a backup. Save and close work first, and ask IT before repairing a managed computer.

Try it: the Date Difference Calculator: days, months, years and weekdays between two dates, with the DATEDIF formulas.

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Sources: Function behaviour and menu paths: Microsoft Support documentation for Excel. Method & sources

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