Safe Mode
If Outlook worked correctly the last time and nothing has changed about your account configuration, then checking if things work correctly in Safe Mode is a good first step. Starting Outlook in Safe Mode will prevent some or all add-ins from being loaded, prevents several settings files from being loaded and turns off the Reading Pane.
To start Outlook in Safe Mode you’ll need to start Outlook with the “safe” switch;
When typing, please note the space between outlook.exe and /safe.