TV Tropes has an extremely odd form of login, and there seems to be no way to recover a lost password or to change an existing password.
It can be reset at http://tvtropes.org/pmwiki/password_reset.php . I don't know if this is new, or the thread is just a manual alternative.
As far as I understand from this forum discussion of TV Tropes, only admins can do that. Just ask them to do it posting a request on that thread.