Remove the application. (but not the profile data) Reinstall from thunderbird.net

I tried that and Thunderbird still does not load

Start *Windows'* safe mode with networking enabled - win10 https://support.microsoft.com/en-us/help/12376/windows-10-start-your-pc-in-safe-mode Still In Windows safe mode, start thunderbird in safe mode - https://support.mozilla.org/kb/safe-mode-thunderbird Does problem go away? - If no, then cause is either: bug in Thunderbird, something (eg a setting, file or folder) in your Thunderbird profile, your mail provider. Please post into topic the contents of Help | Troubleshooting | copy text to clipboard - If yes, the problem is gone, then (still in Windows safe mode) ... start Thunderbird normally -- If problem is still gone, then cause is a program loaded during windows startup. Possibilities include: antivirus SW, virus/malware, background downloads such as program updates -- If problem came back, then cause is likely a Thunderbird add-on - eliminate them by disabling add-ons one at a time in Tools | add-ons | extensions and restarting (or if you have many, disable multiple add-ons at a time) - If results are unclear ... possibilities include temporary conditions such as contention from other running programs, downloads related to windows update, ... Please let us know your findings.