How about reinstalling on top again?
Actually, the first thing you should do is to try to open Outlook in safe mode. In the address bar on the Start menu, simply type outlook.exe /safe. If it opens, you probably are having a problem with an add-in to Outlook (they are there, even if you did not add them yourself). See here on how to do this. Restart Outlook after disabling your add-ins, and add them back one by one until you find the troublesome add-in. Leave that one permanently disabled.
If an add-in is not the cause of the problem, use the software media to run a repair on Outlook. Once the repair is done, re-apply the Microsoft patches for Outlook 2007 and the latest spam definitions, if you are using Outlook’s spam filter.
If still no joy in Mudville, copy your PST to a safe location, uninstall Outlook, run a good registry cleaner to remove all references to Outlook, restart the machine, re-install Outlook and point it to your PST file.