Thunderbird Not Responding How to fix

On Windows, this may be a corrupt index (MSF) folder. Go to run - %appdata%, find your Thunderbird email folder, and rename the suspect msf folder as [foldername].msf.bad
It is often the Trash folder, though sometimes the Inbox folder will go bad.
Restart t-bird and it will rebuild the index.
I keep all of my old email for many years, and this has saved me a number of times.

Have you tried excluding the Thunderbird profile folder from your anti virus scanning. Most lockups like you describe are caused by anti virus scanning, not corrupt files.

@xdeadline, what your results with Matt’s advice?

The fix I described was effective. Otherwise t-bird was dead.