There are quite a few support topics that deal with this https://www.google.com/search?q=%22Your+Thunderbird+profile+cannot+be+loaded.+It+may+be+missing+or+inaccessible%22&ie=utf-8&oe=utf-8

Thunderbird did an automatic update on my system, 10/17/17, and deleted my profile. Gone are all my archived emails and their folder structure, address book, filters for moving incoming mail to the correct folder, the whole kit and kaboodle. And my undelete utility was unable to restore them.

I'm going to go look through the google search Wayne posted, but I want to make sure Mozilla knows how thoroughly they have screwed me, and probably a whole lot of other people. Thanks, guys.

Same damn problem! I am pulling out what hair I have left.

Does http://kb.mozillazine.org/Recovering_a_missing_profile help?

I have tried to follow that exact page. First of all it is just at the edge of my computer expertise. Second I cannot get the profile to open! It goes to Notepad and that is a far as I can get it. Does not open or enlarge - if those are the correct terms. I can see it in Task View and just above taskbar but very small. Thank you