"Crashed"? Do you have a crash report ID?

Or are you using CCleaner?

I run CC cleaner

I have for years and no problems

jacrozie said

I run CC cleaner

For some reason, the latest versions of CCleaner deletes part of the "prefs.js" file in the Thunderbird profile with the mail accounts information. In CCleaner Options|Exclude add the profile folder or the prefs.js file to the excluded list to keep CCleaner from damaging the file in the future. If you have a backup of your prefs.js file, you can copy the good version to your Thunderbird profiles folder and replace the corrupted file.

If you do not have a good copy of the prefs.js file, you can find instructions on repairing or creating a new file here: http://kb.mozillazine.org/Recovering_a_profile_that_suddenly_disappeared