创建新闻模块：部分ADD

At the moment, Im trying to create "news module" on my website, starting with adding news to mysql database but its not working - after hitting button submit nothing happens - no new data in db.

    <?php
          $servername = "localhost";
          $username = "u296093122_admin";
          $password = ".";
          $dbname = "u296093122_datab";

        if(isset($add_n)){
            $conn = new mysqli($servername, $username, $password, $dbname);

          if ($conn->connect_error) {
           die("->Pripojenie neúspešné: " . $conn->connect_error);
                                    }

           $sql = "INSERT INTO Akcie(nadpis, obsah, timestamp)VALUES('$nadpis', '$obsah', NOW())";
           $result = $conn->query($sql);

        if(!$result){
            echo('Error ' . $mysql_error());
            exit();
        }else{
        mysql_close($conn);
        echo('Success!');
            }
    }else{
    ?>
    <form name="form1" method="post" action="<?php echo $PHP_SELF; ?>">
        <table width="50%" border="0" cellspacing="0" cellpadding="0">
            <tr>
                <td>Nadpis:</td>
                <td><input name="nadpis" type="text" id="nadpis"></td>
            </tr>
            <tr> 
                <td>Obsah novinky:</td>
                <td><textarea name="obsah" id="obsah"></textarea></td>
            </tr>
            <tr> 
                <td colspan="2"><div align="center">
                <input name="hiddenField" type="hidden" value="add_n">
                <input name="add" type="submit" id="add" value="Submit">
                </td>
            </tr>
        </table>
    </form>
<? } ?>