My blog's homepage and admin page (and presumably all pages) shows "500 Internal Server Error". I have made no changes to the blog, not even a post, in 3 weeks. Everything else on my website, including other database-using software applications, and a 2nd wordpress installation, still work fine. How can I access the blog if I can't login? (I can use FTP/SecureFTP to make changes, but I don't think FTP can help me assess what I need to change, if anything.) How can I diagnose what is causing the Internal Server Error?