Outlook 2011 Stopped Opening

I have a MacBook Air, Mid 2011 with Mac OS X Lion 10.7.5.  I have Microsoft Office for Mac 2011.

I have been using Outlook successfully for 2/3 years, but suddenly today it has stopped opening.  Other Office software opens.  But when I click on Outlook it appears to start opening (the standard yellow box appears briefly), but then stops.  No error message is seen.

I have restarted the MacBook several times and checked Software Update.

I have followed threads for similar issues and done the following:

- Hold 'Option' key and click on Outlook icon to open Microsoft Database Utility.  I have created a second 'identity', made it the default, and then opened Outlook - successfully (though with no content).  When I reset the default to the original identity I am again unable to open Outlook.

Though I have found threads that suggest taking the above step I have not found anything that then explains what that means, or what to do next.  Some threads seem to say I have to rebuild a database, and others caution against rebuilding a database.  Rebuilding a database sounds like I am going to lose something by doing it - whether it be content, different accounts I have set up within Outlook, rules etc.

Can anyone give me advice please?

JJ

P.S.  Shortly before this Outlook failure I had an error message that required me to switch the MacBook off and on again.  This has been a recurring problem over the last few months (though never previously resulting in an Outlook failure).  The panic report runs 4 pages long and there is no particular error code I can find.