PHP - Moved: Spell Check My Php Code

Hi, I need to insert some code into my current form code which will check to see if a username exist and if so will display an echo message. If it does not exist will post the form (assuming everything else is filled in correctly). I have tried some code in a few places but it doesn't work correctly as I get the username message exist no matter what. I think I am inserting the code into the wrong area, so need assistance as to how to incorporate the username check code.

$sql="select * from Profile where username = '$username';
$result = mysql_query( $sql, $conn )
      or die( "ERR: SQL 1" );
if(mysql_num_rows($result)!=0)
{
process form
}
else
{
echo "That username already exist!";
}


the current code of the form


<?PHP
//session_start();
require_once "formvalidator.php";
$show_form=true;

if (!isset($_POST['Submit'])) {



$human_number1 = rand(1, 12);



$human_number2 = rand(1, 38);



$human_answer = $human_number1 + $human_number2;



$_SESSION['check_answer'] = $human_answer;
}

if(isset($_POST['Submit']))
{





if (!isset($_SESSION['check_answer'])) {
echo "<p>Error: Answer session not set</p>";
}


if($_POST['math'] != $_SESSION['check_answer']) {
echo "<p>You did not pass the human check.</p>";
exit();
}


   $validator = new FormValidator();
    $validator->addValidation("FirstName","req","Please fill in FirstName");







$validator->addValidation("LastName","req","Please fill in LastName");
$validator->addValidation("UserName","req","Please fill in UserName");
$validator->addValidation("Password","req","Please fill in a Password");
$validator->addValidation("Password2","req","Please re-enter your password");
$validator->addValidation("Password2","eqelmnt=Password","Your passwords do not match!");
$validator->addValidation("email","email","The input for Email should be a valid email value");
$validator->addValidation("email","req","Please fill in Email");
$validator->addValidation("Zip","req","Please fill in your Zip Code");
$validator->addValidation("Security","req","Please fill in your Security Question");
$validator->addValidation("Security2","req","Please fill in your Security Answer");
    if($validator->ValidateForm())
    {
        $con = mysql_connect("localhost","uname","pw") or die('Could not connect: ' . mysql_error());
        mysql_select_db("beatthis_beatthis") or die(mysql_error());
$FirstName=mysql_real_escape_string($_POST['FirstName']); //This value has to be the same as in the HTML form file
$LastName=mysql_real_escape_string($_POST['LastName']); //This value has to be the same as in the HTML form file
$UserName=mysql_real_escape_string($_POST['UserName']); //This value has to be the same as in the HTML form file
$Password= md5($_POST['Password']); //This value has to be the same as in the HTML form file
$Password2= md5($_POST['Password2']); //This value has to be the same as in the HTML form file
$email=mysql_real_escape_string($_POST['email']); //This value has to be the same as in the HTML form file
$Zip=mysql_real_escape_string($_POST['Zip']); //This value has to be the same as in the HTML form file
$Birthday=mysql_real_escape_string($_POST['Birthday']); //This value has to be the same as in the HTML form file
$Security=mysql_real_escape_string($_POST['Security']); //This value has to be the same as in the HTML form file
$Security2=mysql_real_escape_string($_POST['Security2']); //This value has to be the same as in the HTML form file



$sql="INSERT INTO Profile (`FirstName`,`LastName`,`Username`,`Password`,`Password2`,`email`,`Zip`,`Birthday`,`Security`,`Security2`) VALUES ('$FirstName','$LastName','$UserName','$Password','$Password2','$email','$Zip','$Birthday','$Security','$Security2')"; 
//echo $sql;
if (!mysql_query($sql,$con)) {

 die('Error: ' . mysql_error());

} else{



mail('email@gmail.com','A profile has been submitted!',$FirstName.' has submitted their profile',$body);

echo "<h3>Your profile information has been submitted successfully.</h3>";
}

mysql_close($con);
        $show_form=false;
    }
    else
    {
        echo "<h3 class='ErrorTitle'>Validation Errors:</h3>";

        $error_hash = $validator->GetErrors();
        foreach($error_hash as $inpname => $inp_err)
        {
            echo "<p class='errors'>$inpname : $inp_err</p>\n";
        }        
    }
}

if(true == $show_form)
{
?>

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