Non-responsive may mean another program is intervening and that is usually the Anti-Virus. What AV are you using ? Do you allow the AV to scan each folder that gets opened or scan emails or scan any folder in your Thunderbird profile ? Test: Restart computer in 'Safe Mode with Networking' mode - you may need to use an ethernet cable to connect computer to router. Then start Thunderbird and see if it works better. Report on results. Regarding Anti-Virus: Set up the Thunderbird profile to be excluded from scans. If you have profile in default location then it this Thunderbird folder to exclude: * C://Users/User name/Appdata/Roaming/'''Thunderbird'''