A few q. Did it work before? Are you more then one user on that PC, with different usernames? If so have you set up TB on all users? Or have you set up TB from one user with different profiles?

Thank you for your reply. There is a one users on the pc.

I reinstalled Mozilla Thunderbird but the problem did not improve.

Run Mozbackup and save your thunderbird profile (all) store it where you could find it Start tb from run (Window-key + R) command: Thunderbird -P Create a new profile and exit it immediately. start MozBackup and restore your saved profile into your new profile

Start TP again from run and set it to open last used profile enter your new profile. Hopefully all is restored

Link MozBackup