What do you mean by "open"? Do you mean that Thunderbird doesn't start at all, or does it open but fails to retrieve email? We need more information. * What version of Thunderbird? * What is your operating system and version? * Do you see any error messages * Did it used to work, then suddenly stop? Have you made any major changes that could affect that? * Is your email account set up in Thunderbird as IMAP or POP3? * Who is your email provider?