No idea myself but the good folks in Google-land suggest the following:
1)Start->run..then type the following -> "Outlook.exe /resetnavpane"
2) it might be a problem with your Outlook profile:
"This happened to me yesterday for the first time after Outlook crashed,
taking down the entire system. Apparently the Outlook profile became
corrupted. I was able to solve it by creating a new profile. Then I opened
my old PST file, made it the default, re-started Outlook, and closed the new
(empty) PST file that Outlook created."
3) Some other thing, most of which seem to be covered here:
http://www.howto-outlook.com/faq/outlookdoesntstart.htm4) Ask Si Pie