I have also heard of this happening when Lightroom encounters a template or preset it doesn't understand. If you have any templates or presets you created (or purchased/downloaded from others), try moving those to see if Lightroom will start when they aren't accessible. (Template and preset locations are also noted in the previous link.) If Lightroom starts after moving those files, you can gradually add them back in until you determine which one is causing the problem. If you do narrow it down, post back - I'd like to get the problematic one for further investigation.