You'll need to give us more information. What version of MySQL are you using? What is the exact error message? What is the HTTP response code? If possible, attach a screenshot.

normally 'Error 500' is caused by a misconfiguration in your .htaccess file, maybe there went sth wrong.

usually you can find it in the root folder of your website - htdocs, public_html or whatever its name may be depends on your configuration.

do you use windows or linux as your server's OS? ... on linux files that have a prefixed dot (like .htaccess) are hidden. so you have to tell your FTP-client to show hidden files as well. if you use the linux console, change to your website-root and type 'ls -asl' that will show you all files in the driectory, including hidden files.

there are several pages on that mod_rewrite/.htaccess topic, because that would be way too much for this forum ;)

you also should check your httpd.conf (apache_install_dir/conf/httpd.conf on Win, /etc/apache2/httpd.conf on most linux systems) if mod_rewrite is properly enabled and so on.

if you find sth similar to

#LoadModule mod_rewrite someweirdfilenamethaiactuallydontremember.so

change it to:

LoadModule mod_rewrite someweirdfilenamethaiactuallydontremember.so

On Linux boxes you may just type 'a2enmod rewrite' as root and restart apache with '/etc/init.d/apache2 restart'