Follow the steps to troubleshoot or repair outlook 365 login:-
From Start select Settings to launch Windows Settings
Choose Apps from Windows Settings. (It might take a few moments for the Apps list to load)
Now find Microsoft Office Desktop Apps on the list and select it.
Select Advanced Options and in the menu that opens choose Repair.
Visit at: http://us-outlookoffice365.com/outlook-office-365-troubleshooting