Start *Windows'* safe mode with networking enabled - win10 http://windows.microsoft.com/en-us/windows-10/change-startup-settings-in-windows-10 Still In Windows safe mode, start thunderbird in safe mode - https://support.mozilla.org/kb/safe-mode-thunderbird

Does problem go away?

this was not helpful. Also, repaired bitdefender, seemed to work for a bit, but tbird started to hang again, and got message 'failed to connect to server', but then I did get messages. Deleted all messages in all folders not needed. Do NOT have an all inboxes subscribed to ( a gmail issue) Have all the correct server settings... Now what?

this was not helpful.

In which way?

What do you mean 'in which way?". They did not fix the problem

Please clearly state what you did and what happened.

I uninstalled an reinstalled. I checked with bitdefender and did all they said..ie disabled everything, then re-enabled one at a time. I deleted all msf (?) files in my tbird profile. I got rid of spam folder (I can go to gmail online and delete it there), I compacted folders. And still it runs slowly at times, says 'not responding' for several minutes before responding.

I uninstalled an reinstalled.

You uninstalled an reinstalled what? Thunderbird? Bitdefender?

Did you follow the steps as per Wayne's instructions? https://support.mozilla.org/en-US/questions/1129031#answer-892929

You can answer that with a simple yes or no.

If 'no', please go through all the steps and report back.

If 'yes', please explain what happened.

I did all that..sorry so long, but holiday away It seemed to fix the problem and it is working ok past few days, but I still get the message..."*****@gmail.com failed to connect to server" which is ridiculous, since I get and receive emails.

Also, minor issue... despite having checked 'delete trash on exit' it isn't

I still get the message..."*****@gmail.com failed to connect to server" which is ridiculous, since I get and receive emails.

That sounds like a temporary connectivity failure. Wrt your anti-virus software follow these generic instructions.

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

Also, minor issue... despite having checked 'delete trash on exit' it isn't

Please start a new topic for this.