Outlook won't start: some solutions!

Outlook is known for it: it regularly happens that, for various reasons not necessarily attributable to Outlook itself, it does not run (or no longer runs) properly...

"Cannot start Microsoft Outlook. Cannot open the Outlook window. ..."

Don't panic: there are simple commands you can run to get back your mailboxes, contacts, calendars, notes, custom manager and other add-ons...

Quite often, the problem lies precisely with add-ons, the small extensions from other software that plug into Outlook to add extra features. Teams, for example, Microsoft's collaboration tool, seems particularly unstable with Outlook, so it is better to disable it there!

First thing to try: start Outlook in safe mode

In the Start menu, search for "Run" or use the Windows + R keyboard shortcut.

Then simply type "Outlook /safe" and confirm. Outlook then starts without its add-ons. A quick trip to File / Options / Add-ins / Go lets you tick or untick add-ins, then restart Outlook normally to see the changes.

Reset the navigation pane

The folder navigation pane on the left regularly prevents Outlook from starting properly.

In the Start menu, search for "Run" or use the Windows + R keyboard shortcut, then run the command "Outlook.exe /resetnavpane"

Repair the Outlook data files (.pst and .ost)

If it is too large or the disk is fragmented, the Outlook data file can become corrupted. In the Office installation folder you will find a program called scanpst. Run it, open your data file (you can find its location through the Mail icon in the Control Panel) and start the repair. I recommend making a copy of this file first!

Recreate the Outlook profile

If you use Outlook as a client and your data is online (webmail, Exchange, Office 365 or another cloud service), the radical solution is to delete the current profile and create a new one. Go to the Control Panel, Mail icon, then Show Profiles, and follow the steps to delete, create or set a default profile! Note that you will need to enter your email credentials again; Outlook will then create a "clean" data file and retrieve your data.

A few useful commands

In the Start menu, search for "Run" or use the Windows + R keyboard shortcut, then run "Outlook.exe" followed by the switch starting with /. Mind the space between outlook.exe and the /, for example: "Outlook.exe /resetnavpane"

/Noextensions: Starts Outlook with extensions turned off, but listed in the Add-In Manager.
/Resetfoldernames: Resets default folder names (such as Inbox or Sent Items) to default names in the current Office user interface language.
/Resetfolders: Restores missing folders for the default delivery location.

For more switches and features, head over to Microsoft.