Hi,
There are two things you can try first: delete the preferences.cfg file from that folder:
* Windows: C:\Documents and Settings\your user name\Application Data\Ableton\Live x.xx\Preferences
* Mac OS X: /Library/Preferences/Ableton
And restart Live. If that does not work, it could mean that one of your plugins is causing a problem. Move the content of your plugin folder to a temporary folder, and restart Live. If it starts, move back the plugins by small numbers to the right folder, and restart Live each time. So you can find which one is a problem.
Other than that, have you tried contacting
[email protected]? If you do so, please provide the information asked for on that page:
http://www.ableton.com/pages/support_contact
Regards,
Amaury