My suggestion: - remove account - exit and restart Thunderbird - create account but OMIT password - enter password when attempting to retrieve messages when Thunderbird prompts for it.

Thanks David. What do you mean by "remove account"? How would I do that? Ted

My inference is you completed setting up the account. If true, then rightclick on account in left folder pane, click 'settings', then scroll down to 'Account Actions' and click to delete account. If account has not been set up, then just exit and restart THunderbird and start over, but without password. In reading your post, it looks similar to other situations where including password when setting up account causes the problem.

OK, thanks. I'll give that a shot. Ted

The account password isn't going to work no matter when you enter it. AT&T accounts require a secure mail key for TB instead of the account password.

https://www.att.com/support/article/dsl-high-speed/KM1010523/

It looks like that worked! At least I now have a home screen. Next I'll see if I can move my inbox etc back into the proper files. Wish me luck. Then all I'll have to contend with is that damned secure mail key.

Thanks again, Ted

Hooray! I transferred my inbox etc and set up a new secure mail key And I just downloaded 44 email messages into Thunderbird. Thanks so much for getting me started.

I do have one last (I hope) question. I don't seem to be able to copy by address book successfully. My notes say it should be a file called abook.nab. But I don't see such a file in this version of Tbird. (It is a different version from what I had a few weeks ago. It looks different.) I saw a file called abook.sqlite and I copied that over, but still no address book entries appear. Any suggestions there?

Thanks again, Ted

The current format is .sqlite, but if it didn't appear after copying it over, both .mab and .sqlite files can be imported in Address Book (see picture).