⚠️

The error you are seeing:

"Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. An unexpected error has occurred."

Why did this happen?

🔍 Simple Explanation

Think of Outlook like a house. Inside the house there are 3 important things:

One or more of these became corrupted (damaged) — usually after a Windows update, a sudden shutdown, or a sync error. Outlook tries to open them, fails, and shows this error. The fix is to throw away the damaged copies and let Outlook build fresh ones.

Step-by-Step Fix

1

Make sure Outlook is completely closed

Before we fix anything, Outlook must be fully shut down.

▶ Press Ctrl + Shift + Esc to open Task Manager. Look for Outlook in the list. If you see it, click on it and press End Task.
✅ If Outlook is not in the list, that's fine — just move on to Step 2.
2

Delete the damaged layout file

There is a small file that saves how your Outlook panels look. When it gets corrupted, Outlook can't start. We need to delete it — Outlook will recreate it automatically.

▶ Press Windows key + R on your keyboard to open the Run box.
▶ Type exactly: %APPDATA%\Microsoft\Outlook and press Enter. A folder will open.
▶ Find the file named Outlook.xml and delete it (press the Delete key or right-click → Delete).
✅ Try opening Outlook now. If it works — great, you're done! If not, continue to Step 3.
3

Delete the damaged Outlook profile (account settings)

If Step 2 didn't work, the profile (your saved account settings) is corrupted. We need to delete it from Windows so Outlook can create a fresh one.

▶ Press Windows key + R, type regedit, and press Enter. Click Yes if asked for permission.
▶ In the address bar at the top, paste this path and press Enter:
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Profiles
▶ Right-click the Profiles folder on the left and click Delete. Confirm with Yes.
▶ Close the Registry Editor window.
⚠️ Don't worry! This only removes Outlook's settings on this PC. Your actual emails are stored on your company's mail server and will NOT be deleted.
4

Rename the damaged email data file

Outlook keeps a local copy of your emails in a file ending in .ost. If this file is damaged, Outlook can't open it. We'll rename it (not delete) so Outlook creates a fresh copy.

▶ Press Windows key + R, type %LOCALAPPDATA%\Microsoft\Outlook, and press Enter.
▶ Find the file ending in .ost (it will have your email address in the name). Right-click it and choose Rename.
▶ Add .bak to the end of the name (e.g. yourname.ost becomes yourname.ost.bak). Press Enter.
✅ The original file is kept as a backup with the .bak extension. Outlook will re-download all your emails from the server.
5

Open Outlook and set up your account again

Now open Outlook normally. Because the old profile was removed, Outlook will show a welcome screen asking you to add your account.

▶ Type your work email address (e.g. yourname@yourcompany.com) and click Connect.
▶ If asked for a password, enter your Windows / company login password.
▶ Outlook will find your company's mail server automatically and start syncing your emails.
✅ The first sync may take a few minutes. Outlook will be usable right away — emails will load in the background.

Quick Checklist

✔ Things to do — in order
1
Close Outlook completely (Task Manager → End Task)
2
Delete Outlook.xml from %APPDATA%\Microsoft\Outlook
3
Delete Profiles key from Registry Editor
4
Rename the .ost file to .ost.bak in %LOCALAPPDATA%\Microsoft\Outlook
5
Open Outlook → add your work email → let it sync
🎉

Outlook should now be working!

Your emails, calendar, and contacts are safe on the mail server.
They will re-appear in Outlook as it syncs. This usually completes within a few minutes.

Frequently Asked Questions

Will I lose my emails if I follow this fix?

No. Your emails, calendar, and contacts live on your mail server (Exchange, Microsoft 365, Gmail, etc.), not just on your PC. Deleting the local profile, layout file, or renaming the .ost file only clears the local cache — Outlook re-downloads everything fresh once you sign back in.

What if Outlook still won't open after all 5 steps?

Try running Outlook in Safe Mode (hold Ctrl while double-clicking the Outlook icon) to rule out a misbehaving add-in. If it opens fine in Safe Mode, disable your add-ins one by one from File → Options → Add-ins. Still stuck? A Quick Repair via Control Panel → Programs → Microsoft Office → Change is the next step.

Is it safe to delete the Outlook profile from the Registry?

Yes — deleting the Profiles key under HKEY_CURRENT_USER only removes Outlook's local account configuration on that one PC. It does not touch your mailbox, emails, or any server-side data. Outlook will simply prompt you to set the account up again.