Outlook won't open

Hello,

This situation is usually caused by a corrupted Outlook profile.

You can try creating a new Outlook profile:

Open Control Panel → Mail → Show Profiles → Add

After adding a new Outlook profile, try starting Outlook with the new profile.

The error "Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened" is a common startup issue in classic Outlook for Windows.

Try these steps in order:

1. Reset the Navigation Pane This fixes many "cannot open the Outlook window" or "can't open folders" errors.
   1. Close Outlook.
   2. Press Windows key + R.
   3. In Open, type:

            Outlook.exe /resetnavpane
      

   4. Select OK and let Outlook start.
2. Start Outlook in Safe Mode (to bypass add-ins)
   1. Right-click Start and select Run.
   2. Type:

            Outlook.exe /safe
      

   3. Select OK. If Outlook opens in safe mode, disable problematic add-ins using the guidance under More on starting Outlook in safe mode and disabling add-ins in the linked article.
3. If the error text mentions Exchange or "set of folders cannot be opened" In some cases, especially with Microsoft 365 accounts, the error can be related to an Exchange Online service issue. If the detailed error (for example from logs or traces) shows:
   • Authentication concurrency limit is reached or
   • Microsoft.Exchange.RpcClientAccess.ServerTooBusyException
   then:
   • Use Outlook on the web (OWA) or new Outlook for Windows as a workaround.
   • From the Microsoft 365 Admin portal, open a support case so Exchange Online support can request a service-side change.
4. If Outlook still will not open
   • For older Outlook versions (such as Outlook 2010) where data files were moved or changed manually, restore or move the .ost files back to their original path under C:\Users\{username}\AppData\Local\Microsoft\Outlook, or temporarily move them to the desktop and restart Outlook so it can recreate them.
   • If nothing helps, a full repair or reinstall of Office/Outlook may be required, as shown in the Q&A example where uninstalling and reinstalling Microsoft 365 fixed Outlook not opening.

If the problem persists after these steps, use the community links in the referenced articles to post full error text and environment details for further help.

References:

• I can’t start Microsoft Outlook or receive the error “Cannot start Microsoft Outlook. Cannot open the Outlook Window”
• Open Outlook in safe mode
• Error when opening classic Outlook: "Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. The attempt to log on to Microsoft Exchange has failed."
• What if Outlook can not open after the failure of transferring Outlook related files?
• What to do when Outlook will not open on my PC? - Microsoft Q&A