Well this sucks. I just got done writing an article, and all of the sudden my entire site is down. Really can't get to the mambo admin panel considering EVERYTHING is down. I have no experience with this, so I hope things fix themselves, otherwise I'm going to have to start with a fresh copy of mambo (I JUST set it up and tweeked it, so no backup yet)
well look if you didnt add an htaccess file to it which causes the error. also check if the file permissions on public_html are correct and not running any other index file that may cause the error.
That's a configuration error, usually caused by bad scripts, not the server, though it can be a server issue.
SSH to your site or FTP up an .html file (no script) and see if it shows... then do a BASIC php file, like phpinfo.php that contains <?php phpinfo(); ?> and upload that to see what's going on.
Also check your scripts (.php files) to ensure they're at 755 permissions.