Outlook won't open, freezes, or sits on "Loading profile"

Steps

1. Make sure it isn't already running in the background: press Ctrl + Shift + Esc, find Microsoft Outlook in the list, click it and End task. Then try opening it again normally.
2. Start in safe mode: hold down Ctrl on the keyboard while you click the Outlook icon. Click Yes to "start in safe mode". If Outlook opens this way, an add-in is the problem.
3. In safe mode: File → Options → Add-ins. At the bottom, next to Manage: COM Add-ins, click Go. Untick everything, click OK, close Outlook and open it normally. If that fixes it, re-tick add-ins one at a time to find the culprit (it's often an old antivirus or PDF add-in).
4. Still won't open? Restart the computer and try once more before going further — a Windows update in progress can hold Outlook hostage.
5. Check for updates: in any Office app that does open (Word), File → Account → Update Options → Update Now.

If that didn't work

• The next step is a fresh Outlook profile (Control Panel → Mail → Show Profiles → Add). It's safe with modern accounts (Microsoft 365, Outlook.com, Gmail) because the mail is on the server — but with older POP accounts it needs care so the local mail file is reattached. That's a good point to stop.
• If it's the new Outlook (the blue-and-white one) that's misbehaving, you can switch back to classic Outlook with the toggle at the top right for now.