ok Diagnostic time.

I assume here your still using windows XP (Windows NT 6.0)

in the run box on the start menu type %appdata%\thunderbird and press enter. In the explorer window that opens select the profiles folder Then the folder that ends in default. Open the mail folder now this next folder name is either Local folders or the name of your mail server

Locate a file called inbox. it will have another called inbox.msf.

What size is the inbox file?

I could go further. But I think this better be staged. What come next depends a lot on the actual size.

The inbox file is 313,539 KB.

That is a very long way from the 4Gb limit imposed by XP

ok. With Thunderbird closed. move that file to your desktop and delete inbox.msf.

Restart Thunderbird. Does it start is the obvious question?

Note that is is possible moving or copying the file will also cause a crash. If that is the case, your hard disk contains file allocation errors In accessories > system tools on your start menu there is a check disk for errors option if I recall correctly

Thanks, the problem is fixed.