Try running a quick repair to see if that resolves the issue. You can try the quick repair first and if it is still happening you can try the online repair. Before doing this though you’ll have to make sure you save the work of any Office application you currently have open. To run the repairs, you- click on start->type “apps and features” or “add or remove programs”-> find “Microsoft Office 365 Business-en-us” ->click on it-> select “modify”.