So, second part.

Now i got the information for that mysql database but each time I incorporate a mysql function within the wordpress HTML editor (with professional-php enabled) the website is empty (aside from the conventional design and also the title from the site within the tab is "Site not found" when before everything labored great.

Any idea? What's WordPress problem?

    if(isset ($_POST['name']))
        if($_POST['name'] == "" || $_POST['adresse1'] == "" || $_POST['adresse2'] == "" || $_POST['land'] == "" || $_POST['tel'] == "" || $_POST['email'] == "" || $_POST['interessen'] == "")
            echo "Mindestens eine Angabe fehlt leider.";

echo "<br/><br/><a href=\"javascript:history.back()\">Zurück</a>";
            mysql_connect("xx","xx","xx") or die(mysql_error());

This really is my code, $_Publish works okay and also the form can also be proven. However when I use a mysql_hook it up loads no text and do not give a mistake report too. And also the title within the tab bar changes to "Site not found". However with phpmyadmin i'm able to access the database.

Enable wordpress debug-mode and check out your error-log. Make it possible for debug-mode, place the following to your wordpress-config.php:

/** Debugging WP */
define('WP_DEBUG', true);
define('WP_DEBUG_DISPLAY', true);
define('WP_DEBUG_LOG', true);
define('SCRIPT_DEBUG', true);

Furthermore consider the error-log of the webserver.