Do you have windows updates waiting to install? If yes, install them. Leaving updates waiting causes outlook's behavior to degrade.
Did you try repairing Office install? Quick repair should be sufficient. Right click on the start menu and choose Apps & Features, find and select the Office installation. Choose Modify then select the Quick repair option. Use the Quick Repair option first as it will fix many things and complete fairly quickly.
If neither of the above (or a reboot) doesn't fix it, when did the problem start?