Hi, welcome to the forums.
Do a search of these forums for 'thunderbird' and 'inbox' (without the quotes) as a number of people have deleted their inbox (contrary to various warnings in the help/faqs of the email program). In one of the threads there is a suggested program to undelete files.
If you find it and recover it you will have to manually find the infected email (check each email in turn) and delete it manually.
Best advice in never use your inbox as a storage device, use it to check emails and then put them in other more appropriate folders for the subject of the email. That way if you have a deletion/corruption problem with your inbox (it seems to happen more frequently to the inbox), big deal you only lose a few emails.
Check out this
Links Thread, you might find a program of use there also.
HTH David