I doubt that this will help but I don't have anything else to offer:
Clear the browser cache and the Windows Temp directory.
Shutdown any anti-virus software you are running.
Download a new copy of the full installer from
http://www.mozillamessaging.com/en-US/thunderbird/
Delete the directory C:\Program Files\Mozilla Thunderbird
Run the installer.
Restart the anti-virus program.
Note that your saved messages, address books, settings, passwords, etc (if any) are stored in a different directory from the program files and will not be removed by deleting the directory identified above.
This thread
http://forums.mozillazine.org/viewtopic ... 5#p5239885 has a more detailed version of the above instructions if needed.