So how far does it get? Do you actually see the Ableton logo/start screen at all before it quits? No Windows error messages? You might check in Event Viewer (Start > Programs > Administrative Tools > Event Viewer), both system log and applications and see if there's any reference to ableton.exe or similar.
Have you tried uninstalling and reinstalling Ableton? Did you install any 3rd party plugins that might be causing it to choke? If you haven't yet, you might try holding down Alt during startup to disable plugins and see if it makes any different. That'll tell you whether it's plugin related at least. Also might try [Only registered and activated users can see links. Click here to register]
It honestly sounds like something got corrupted along the way and I'm wondering if a reinstall wouldn't fix it up. If not it at least rules that out and points to something other than the program itself.