Outlook email not starting up

Hi Kandice

From your post, I understand how inconvenient it is when Outlook suddenly won’t open, especially when it was working fine just the day before.

I can see there's a Q&A Assist reply under your post. To avoid repeating the same steps, could you please let me know whether you already tried those yet, and if so, what happened?

In addition, please try a Microsoft 365 app repair, which can fix startup issues caused by damaged program files:

• Close all Office apps.
• Open Settings > Apps > Installed apps
• Find Microsoft 365, select Modify
• Choose “Quick Repair” first.
• If that doesn’t help, repeat and choose “Online Repair” (this reinstalls the apps; sign‑in will be required).

Please feel free to let me know how it goes. Thank you for your time and understanding.

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Follow these steps to troubleshoot Outlook not starting after a reboot:

1. Run the Outlook startup troubleshooter (classic Outlook)
   • If using classic Outlook for Windows with Microsoft 365 for home or business, run the classic Outlook startup troubleshooter, which can automatically diagnose and fix several common startup issues.
   • Requirements:
     • Windows 10 or higher.
     • Must run on the same PC where Outlook is installed.
   • Steps:
     1. Go to the classic Outlook startup troubleshooter via the “Start” button described in the article.
     2. Allow the site to open Get Help when prompted.
     3. Follow the prompts in Get Help and apply any fixes it suggests.
2. Try starting Outlook in Safe Mode
   • This checks whether an add-in is preventing Outlook from starting.
   • Start in Safe Mode:
     1. Press Windows + R to open the Run dialog.
     2. Type Outlook /safe and select OK.
     3. In the Choose Profile dialog, accept the default profile name and select OK.
     4. Enter the email password if prompted and select Accept.
   • If Outlook opens in Safe Mode, the issue is likely caused by an add-in.
3. Disable all add-ins (if Outlook opens in Safe Mode)
   1. In Outlook (Safe Mode), go to File > Options > Add-ins.
   2. At the bottom, ensure Manage is set to COM Add-ins, then select Go.
   3. Record which add-ins are enabled (or take a screenshot).
   4. Clear all check boxes to disable all add-ins, then select OK.
   5. Close Outlook (File > Exit).
   6. Start Outlook normally (without /safe).
   • If Outlook now starts, re-enable add-ins one at a time, restarting Outlook after each, until the problematic add-in is identified. Leave that add-in disabled.
4. Create and test with a new Outlook profile
   • If Outlook does not start even in Safe Mode, the Outlook profile may be corrupted.
   • Follow the steps in “Create an Outlook profile” to create a new profile.
   • Then:
     1. Restart Outlook.
     2. In the Choose Profile dialog, select the new profile.
     3. Select OK.
   • If Outlook starts normally with the new profile, the original profile is corrupted. Use the new profile going forward. Before removing the old profile, back up data files, because removing a profile deletes offline cached content.
5. Repair Outlook data files (if profile or data corruption is suspected)
   • If Outlook data files (.pst or .ost) are corrupted, use the Inbox Repair Tool (scanpst.exe) as described in “Repair Outlook Data Files (.pst and .ost)”.
   • Close Outlook before running the tool, then follow the repair instructions in the referenced article.

If these steps do not resolve the issue, use the Outlook troubleshooters listed in “Issues sending and receiving email” (they also cover broader Outlook problems) and, if needed, contact support from that page.

References:

• I can’t start Microsoft Outlook or receive the error “Cannot start Microsoft Outlook. Cannot open the Outlook Window”
• Issues sending and receiving email