Go to a command line and type in this;
and it should open up the manager for all thunderbird profiles. It's possible you have more than one profile and something reset it to a default instead of your actual profile. If so, you can then choose the one you want.
Also can run a search on your entire drive starting from root directory for "Inbox" or "Sent" or "Drafts" and such like to find where your emails are stored.
If you use IMAP account connection, such as yahoo mail, others, it's possible the inbox using webmail access erased it, and then it synced what you had on your computer, causing it to disappear. So, open the IMAP email program using webmail access and see if somehow it all got dumped into the Bulk, Junk, Trash, Deleted, or similar folder. If so, save it back to the INbox and remember to create a second fake mail account in Thunderbird where you can at times move things from the IMAP account to avoid that from happening to your older "archived" messages.