PHP script not inserting form data to database

I'm having trouble inserting form data into my database. I can connect to the database as it does not throw up an error but no information is being inserted. Below is my code, any help would be appreciated.

<?php  
// string checking
function isValid($str) {
  if(!preg_match('/[^A-Za-z0-9.-]/', $str)) {
  return true;
  } else {
    return false;
  }
}


// Check for form submission
if(isset($_POST['submit'])){

// Get the POST data
$agree = $_POST['agree'];
$firstname = $_POST['firstname'];
$surname = $_POST['surname'];
$business = $_POST['business'];
$state = $_POST['state'];
$email = $_POST['email'];

// If the T&C box has been ticked
if($agree){

  // Validate the POST data
  $validationError = '';

    // Name Validation
    if($firstname == ''){
      $validationError .= "Please enter your first name.\n";
    } else {
      if(is_numeric($firstname)){
        $validationError .= "The first name you have supplied cannot contain numbers.\n";
      }
      if(strlen($firstname) > 50) {
        $validationError .= "The first name you have supplied must be less than 50 characters.\n";
      }
      if(strlen($firstname) < 3) {
        $validationError .= "The first name you have supplied is too short.\n";
      }
      if(isValid($firstname) == false ){
        $validationError .= "The first name cannot contain special characters.\n";
  }
    }

if($surname == ""){
      $validationError .= "Please enter your Surname.\n";
    } else {
      if(is_numeric($surname)){
        $validationError .= "The Surname you have supplied cannot contain numbers.\n";
      }
      if(strlen($surname) > 50) {
        $validationError .= "The Surname you have supplied must be less than 50 characters.\n";
      }
      if(strlen($surname) < 3) {
        $validationError .= "The Surname you have supplied is too short.\n";
      }
      if(isValid($surname) == false ){
        $validationError .= "The Surname cannot contain special characters.\n";
  }
    }


if($state == ''){
      $validationError .= "Please select your state.\n";
}

    // Email validation

    // Function to validate email addresses, taken from here: http://www.linuxjournal.com/article/9585
    function check_email_address($email) {

      // Set up regular expression strings to evaluate the value of email variable against
      $regex1 = '/^[_a-z0-9-][^()<>@,;:\\"[] ]*@([a-z0-9-]+.)+[a-z]{2,4}$/i';

      // Run the preg_match function on regex 1
      if (!preg_match("/([\w\-]+\@[\w\-]+\.[\w\-]+)/",$email)) {
           return false;
      } else {
          return true;      
      } 
    }

    if($email != ''){
      if(!check_email_address($email)) {
        $validationError .= "The email address does not appear to be correct, please try again.\n";
      }
    } else {
      $validationError .= "Please enter your email address.\n";
    }

  //Start the mySQL connection

  if($validationError == ''){
    $link = mysql_connect('localhost', '--removed--', '--removed--');

    if (!$link) {
      $validationError .= "There was an error connecting to the database. Please contact us so that we can fix the problem.\n";
    } else {

      // Select the db
      mysql_select_db("keyinv_seminar", $link);

      // Check for an existing entry under that email address
      $checkQuery = 'SELECT * FROM seminar WHERE email="' . mysql_real_escape_string($email) . '"';
      $result = mysql_query($checkQuery, $link);

      if (mysql_num_rows($result) != 0) {
        $validationError .= "There is already an entry in the competition, using that email address.\n";
      } else {
        // There is no existing entry, update the db
        $insertQuery = "INSERT INTO seminar (firstname, surname, business, state, email) VALUES ('" . mysql_real_escape_string($firstname) . "', '" . mysql_real_escape_string($surname) . "', '" . mysql_real_escape_string($business) . "', " . mysql_real_escape_string($state) . ", '" . mysql_real_escape_string($email) . "')";

        $result = mysql_query($insertQuery, $link);

      }

      // Close the connection
      if($link){
        mysql_close($link);

        if($validationError == ''){
          header('Location: thankyou.php');
        }
      }
    }
  }
} else {
  $validationError = "You must accept the Terms and Conditions \nin order to enter this contest.";
}
}
?>