Unfortunately there is a bug in the Office 2013 September Public Update which you may notice when you start Outlook and see an empty folder pane:
Don’t worry, your folders are not lost, you can minimize the unused screen estate, and you can even work with your folders using the minimized features of the folder pane. So Outlook remains usable, but very uncomfortable.
Microsoft confirmed the bug and they are working hard to update the update: Outlook 2013 Folder Pane Disappears After Installing September 2013 Public Update
So far the solution is to uninstall the KB2817630 update from the Programs and Features window. However, it is tricky! The same update appears twice in the list and you have to uninstall both:
The other trick is that after the removal the patch may be reinstalled when your system is updated next time. Although Microsoft removed the patch from the Windows Update servers, if you have a local WSUS installation you have to manually Decline this update.