impossibilité d'ouvrir thunderbird

You would not lose your folders, as an uninstall leaves the profile intact, but that should not be necessary. If the account is refusing the password, you might try removing the old password. You can do that by clicking settings, then privacy&security, then click savedpasswords and then showpasswords and the highlight the rows for the account and delete them. That would give the opportunity usually to be prompted for new password.