Sometimes a user will see a box open up when opening Outlook, it will say something like "Access denied", or "Set of Folders Cannot Be Opened".
In just a couple of steps, this can be fixed.
1) In the search bar/clicking the magnifying glass to open search, type "Control Panel" and open the control panel.
2) Click the "view by" in the upper right and select "Small icons":
3) Click the Mail (Microsoft Outlook) icon:
4) Click Show Profiles:
5) There should be just one listed. Click "Remove":
6). Close all the boxes and Control Panel, and re-open Outlook, it will download your emails, calendar, contacts and settings again, and then open and repopulate your emails and calendars etc.