Outlook won't open, splash screen comes up briefly and then disappears again and the program quits

My mother's installation of Outlook 2011 has suddenly stopped working.  When she tries to run it, the splash screen comes up briefly (like for about a second or less) and then disappears again and the program quits.  This is all that it does.  It does not display any kind of error message.  It just quits.  There is a file sitting on her Desktop titled Sent Items.mbox and the Get Info window and icon suggest that this file is connected to Outlook.  I assume that this is the file containing her sent emails, but I can’t find where it is supposed to go.

What I am think is that my mom was poking around in folders that she should not have been in an accidentally moved this file out of its correct location and that Outlook, not finding it, is simply quitting.  Is this what is happening?  Can someone tell me where this file is supposed to go?