Please Start *Windows'* safe mode with networking enabled - win10 https://support.microsoft.com/en-us/help/12376/windows-10-start-your-pc-in-safe-mode - win8 https://support.microsoft.com/en-us/help/17076/windows-8-startup-settings-safe-mode - win7 https://support.microsoft.com/en-us/help/17419/windows-7-advanced-startup-options-safe-mode#start-computer-safe-mode=windows-7 - XP https://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/boot_failsafe.mspx

Still In Windows safe mode, start thunderbird in safe mode - https://support.mozilla.org/kb/safe-mode-thunderbird

Does problem go away? Please post to let us know results.

ThunderBird not responding Fix (Safe Mode) Thunderbird is sensitive to other program activity. Please start *Windows'* safe mode with networking enabled - win8 https://support.microsoft.com/en-us/help/17076/windows-8-startup-settings-safe-mode Still In Windows safe mode, start thunderbird in safe mode - https://support.mozilla.org/kb/safe-mode-thunderbird We did as this instructed: call our computer tech, Tech said this safe mode is a band-aid fix, and the TREND MICRO security no longer works if running in safe mode. What security is compatible with Thunderbird?

Safe mode is primarily a diagnostic tool, which your tech should understand.

Trend certainly won't be running (unless you started it manually) if you started Windows in safe mode. That's by design. As for what to run or how to tweak AV, see https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues