I have 3 IMAP accounts - subject title line downloads into Thunderbird with blank message

For all 3 IMAP accounts?

I have 1 POP account - it won't even download a subject line.

See https://support.mozilla.org/kb/cannot-receive-messages

I am not able to send anything.

See https://support.mozilla.org/kb/cannot-send-messages

yes - all 3. I tried deleting one account from Thunderbird and reinstalling it, but that didn't help.

Test: Start computer in 'Safe Mode with Networking' mode. Start Thunderbird Report back on results.

I did as you said - started computer in Safe Mode with Networking and Thunderbird was fine - could send and receive messages. I put it back in normal mode and now nothing works again.

Windows safe mode disables anti-virus software, which is most likely the culprit. These are some generic suggestions to avoid problems with anti-virus software.

Create an exception in your anti-virus software for the Thunderbird profile folder, so that the anti-virus real-time scanner will not scan it. http://kb.mozillazine.org/Profile_folder_-_Thunderbird

Don't let your anti-virus software scan incoming and outgoing messages.

Don't let your anti-virus software scan attachments.

Don't let your anti-virus software intercept your secure connection to the server.

Remove any add-ons your anti-virus software may have installed in Thunderbird.

Keep it working. http://kb.mozillazine.org/Keep_it_working_-_Thunderbird

And last but not least, backup your Thunderbird profile on a regular basis. https://support.mozilla.org/kb/profiles-where-thunderbird-stores-user-data#w_backing-up-a-profile

I found the Thunderbird profile folder - how do I create an exception?

You'd need to check with your anti-virus software vendor. Presumably there is a support forum for it as well. And this article may help. https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues

I turned off the Avast email shield and all is working perfectly - thanks to all of you who were kind enough to explain things! I thought I was going to have to give up Thunderbird, and I really didn't want that to happen! Thanks again!

Nothing works so there is no point in sending me an email to set up a time to have a chat......Nothing works. Won't send, won't receive....You can contact me on waiotahi6@gmail.com?

janetandian When you post a comment in someone else's question, you are are specifically sending them an email and anyone else who just happens to be following the question. I got email because I had forgotten to stop following a question with a 'Chosen Solution'.

re:Nothing works so there is no point in sending me an email to set up a time to have a chat. No one would send you an email setting up a time to chat anyway. This is a public forum and all reponses are via this forum. You would get an email sent to the email address you used when creating a profile to post comments in this forum.

If the 'Chosen Solution' does not work for you then please create a question of your own. Also please tell the forum what OS you use, what version of Thunderbird and what Anti-Virus product you use.