Selam
Muhtemelen MySQL ile işlem yapmaya çalıştığınızdan ötürü hata verdiğini düşünüyorum.
Güncellenmesi gereken yerleri MySQLi ile değiştirdim ve test ettim sağlıklı çalışıyor.
Fakat bu dosya eğer bir script'in kurulum dosyası ise onun çalışmayacağını düşünüyorum.

<form action="" method="POST">
    <table width="300" border="0" align="center" cellpadding="0" cellspacing="1" bgcolor="#CCCCCC">
        <tr>
            <td colspan="3">
                <p style="text-align:center;"><strong>Admin Login</strong></p>
            </td>
        </tr>
        <tr>
            <td>
                <table width="100%" border="0" cellpadding="3" cellspacing="1" bgcolor="#FFFFFF">
                    <tr>
                        <td align="center">Admin Username <input name="myadminuser" id="myadminuser"></td>
                        <td align="center">Admin Password <input name="myadminpass" id="myadminpass"></td>
                    </tr>
                </table>
                <br>
                <table width="500" border="0" align="center" cellpadding="0" cellspacing="1" bgcolor="#CCCCCC">
                    <tr>
                        <td colspan="3"><p style="text-align:center;"><strong>Sql Infomation</strong></p></td>
                    </tr>
                    <tr>
                        <td>
                            <table width="100%" border="0" cellpadding="3" cellspacing="1" bgcolor="#FFFFFF">
                                <tr>
                                    <td>Host name <input name="myhostname" id="myhostname"></td>
                                    <td>Database Name <input name="mydatabasename" id="mydatabasename"></td>
                                    <td>Username <input name="myusername" id="myusername"></td>
                                    <td>Password <input name="mypassword" id="mypassword"></td>
                                </tr>
                            </table>
                        </td>
                    </tr>
                </table>
            </td>
        </tr>
    </table>
    <?php
        if (isset($_POST['Install'])){
            echo '<center>';
            echo 'Creating settings for Sql....<br>';
            $buffer = '<?php' . "\n";
            $buffer .= '$host=' . chr(34) . $_POST['myhostname'] . chr(34) . "; \n";
            $buffer .= '$username=' . chr(34) . $_POST['myusername'] . chr(34) . "; \n";
            $buffer .= '$password=' . chr(34) . $_POST['mypassword'] . chr(34) . "; \n";
            $buffer .= '$db_name=' . chr(34) . $_POST['mydatabasename'] . chr(34) . "; \n";
            $buffer .= '$tbl_name=' . chr(34) . 'members' . chr(34) . "; \n";
            $buffer .= '$table=' . chr(34) .'Account' . chr(34) . "; \n";
            $buffer .= '?>' . "\n";
            file_put_contents('config.php', $buffer);
            echo 'Sql Settings saved! <br>';
            echo 'Testing Sql Settings.....<br>';
            $con = new mysqli($_POST['myhostname'],$_POST['myusername'],$_POST['mypassword']) OR die('Could not connect');
            echo 'Sql Connection was successful<br>';
            echo 'Creating tables 1/3' . '<br>';
            $con->query('CREATE DATABASE ' . $_POST['mydatabasename']);
            $con->select_db($_POST['mydatabasename']);
            $con->query("CREATE TABLE admins (username varchar(255),password varchar(255))");
            echo 'Creating tables 2/3<br>';
            $con->query('CREATE TABLE `Cheats` (
                `id` int(11) NOT NULL AUTO_INCREMENT,
                `cheatname` varchar(255),
                `cheatgame` varchar(255),
                `cheatcoder` varchar(255),
                `lastupdated` varchar(255),
                `status` varchar(1),
                `proc` varchar(50),
                `dlurl` varchar(255),
                PRIMARY KEY (`id`)
            )');
            echo 'Creating tables 3/3<br>';
            $con->query('CREATE TABLE `Settings`(
                `ID` int(1) NOT NULL,
                `MOTD` varchar(255) NOT NULL,
                `Version` varchar(255) NOT NULL,
                `Download` varchar(255) NOT NULL
            )');
            echo 'Done creating tables<br>';
            echo 'Adding Admin Login<br>';
            $con->query("INSERT INTO admins (username, password) VALUES ('" . $_POST['myadminuser'] . "', '" . $_POST['myadminpass'] . "')");
            $con->query("INSERT INTO Settings (ID, MOTD, Version, Download)VALUES('1','vCheat Loader','','')");
            $con->close();
            echo 'Admin account created<br>';
            echo ('Done!, Please delete ' . chr(34) . 'install.php' . chr(34));
            echo '</center>';
        } else {
            echo '<br>';
            echo '<center><input type="submit" name="Install" value="Install"></center>';
        }
    ?>
</form>