Read this. http://kb.mozillazine.org/Recovering_a_profile_that_suddenly_disappeared

Thanks, Airmail. Thunderbird is back in operation.

Hi Jack :)

What exactly did you need to do to get back in business?

Hi Wayne, I don't remember exactly what was on the window that came up when I tried to open Thunderbird. It did ask if I wanted to create a new account. It also had an option to use an existing account. I chose that, and it asked for the email address and the name. I didn't remember the name but put in something close. It also asked for some settings and gave some options. I put in the info as best I could remember. Then Thunderbird came up. I made some changes to the account settings to match another Thunderbird setup on another computer. The address book, inbox and trash seem to be ok. The sent mail and archives are empty - they contained emails previously.