all of a sudden that messages could not be sent. So I created another account under the same email and password

It would have made more sense to troubleshoot the actual problem.

I got my inbox but, no other folders and no emails appear in the 'sent' box.

This is the way POP works, all you see on the server is Inbox. Messages you send are copied to the local Sent folder, assuming you told Thunderbird to place a copy there in your Account Settings.

Now I have two accounts

I don't think messing with two IMAP accounts for the same user ID will do you any good. Delete one of them and troubleshoot the one left.

but none show previous sent emails as well as other folders.

You can login to your account via webmail. What you see on the server via webmail is what's left, and this should also show up in Thunderbird.

Do you have a backup of your missing messages?

Thanks. Late yesterday I deleted one account. I suppose I did the right delete as everything else came back up!