Please help: Thunderbird portable crashed & broken

Hello experts,

I had a computer crash and as a result, my thunderbird portable has suffered. When I start it, it offers me to set up an account. On the other hand, also given the size of the folders, all mail and so on still seem to be there. So I presume it must be my profile or so that is damaged / gone.

Which files(s) should I check for existence or integrity to overcome this problem? I also might still have an older copy of my thunderbird which I could activate, however I would lose all mails since that backup, and thus would rather extract from it any missing or damaged file. If I knew which ones, that is ...

Thanks in advance for all help!
Chris