Thunderbird Email messages unavailable


New Email
I am using Thunderbird Email App and needed to change from POP3 to IMAP. Current provider is Cox Communications. I could not find a way to make changes via the Tools, Account Settings, Server Settings/Outgoing Server current settings. I used automatic account configuration and after completed all of my Inbox and Sent mail boxes were empty. Most of my subfolders were there, but only had emails up to 2012, which I believe had to do with the fact that I must have done an archive back then. I had completed a System Backup a month ago using Microsoft's Backup and Restore utility. When I went to my backup only the archived emails existed which makes me believe that the system backup does not backup Thunderbird emails (I have since installed the App for backing up and restoring emails). My question is: Are my non archived emails on my system somewhere that I can not access through normal file/folder list or searches? I have Windows 7 Professional installed on my laptop. Also, it appears that the Address Book is up to date.