A Microsoft file hosting and synchronization service.
In any O365 Component > Help > Contact Support
Assuming it worked before start with the basic repair
Restart the PC, once fully loaded, repair Office,> Apps & Features>Select Office your version>Modify /Repair, once the repair completes re-test (Quick repair)
O365 when installed under a Win user admin account, and run from that admin account, auto logs in when the PC is started. There is no separate login for any component.
Win search for Word > Resulting shortcut > Rt click > Pin to task bar > start Word from that shortcut (hover mouse over the shortcut gives access to the 10 most recent docs)