Try removing t-bird, download and re-install. Your settings, etc should be saved.

If you have any add-ons and you still have the problem, try disabling the add-ons one at a time.

The suggestion to move to google apps was because you really want an imap email server, and all that's currently available to you is pop. An imap server won't have these issues even if you have multiple email clients running. It's up to you if you want to stick with a pop server. If you think that's too complicated, I don't know what to tell you. You are trying to fit a round peg into a square hole, and of course that doesn't work.

-David