If you want a fully clean install, remove the ...appdata\roaming\thunderbird folder, not just the profile folder. And then reinstall. Do you have the old profile? Is the old computer still available? The cleanest install would be to - do fresh install of thunderbird and exit - on old computer, with Thunderbird not running, copy c:\users\<yourid>\appdata\roaming\thunderbird to USB stick - on new computer, copy that thunderbird folder to c:\users\<yourid>\appdata\roaming, and allow the overwrites. - start thunderbird.

Thank you David. I was messing with this all night. Your instructions were far clearer than the one I got from the website. I uninstalled Thunderbird again, deleted the Thunderbird folder in roaming, copied the thunderbird directory from a usb drive, and everything came up perfectly.

Thanks for sharing the good news.  :)

TIP: Now that it's running properly, I encourage periodically doing a backup with same steps: - exit TB - copy the ...alppdata\roaming\thunderbird folder to external drive - if need to ever restore, copy the backup to the ...appdata\roaming folder Most problems we see are because there was no backup .