Login with Sha256

Good afternoon everyone,

I have a problem that has intrigued me for a few days now, my boss and stage supervisor proposed me to do an increased security in the site and for this I would have to use a Hash of words passes, after much research I was unable to log into previously "encrypted" accounts and can not find a way to find my problem.

Log page

include("connect.php");

function generateSalt(){
  $characters = '0123456789abcdef';
  $length = 64; 

  $string = '';
  for ($max = mb_strlen($characters) - 1, $i = 0; $i < $length; ++ $i)
  {
    $string .= mb_substr($characters, mt_rand(0, $max), 1);
  }
  return $string;
}


$userAccountInput = $_POST['userName'];
$userPasswordInput = $_POST['pass'];
$salt = generateSalt();
$hash = hash_hmac("sha256", $userPasswordInput, $salt);

$sql = "INSERT INTO username VALUES (NULL,'$userAccountInput','$salt','$hash');"; 

$resultado = mysql_query ($sql);

Login Page

function testPassword($fPassword, $fSaltFromDatabase, $fHashFromDatabase){
              if (hash_hmac("sha256", $fPassword, $fSaltFromDatabase) === $fHashFromDatabase){
                  return(true);
                  }else{
                  return(false);
  }
  }


function SignIn() 
{ 
//session_start(); 
if(!empty($_POST['userName']) || !empty($_POST['pass'])) 
{

                $query = mysql_query("SELECT * FROM username where userName = '".$_POST['userName']."'") or die(mysql_error()); 
                $row = mysql_fetch_array($query) or die(mysql_error()); 

                //$userAccountInput = $_POST['userName'];
                $userPasswordInput = $_POST['pass'];
                $saltFromDatabase = $row['salt'];
                $hashFromDatabase = $row['hash'];

                $var_dump($row);

                if(testPassword($userPasswordInput, $saltFromDatabase, $hashFromDatabase)){
                    echo "<script type='text/javascript'>alert('LOGIN COM SUCESSO!')</script>";
                    header('Location: ./clientes.php');
                }else{

                    echo "<script type='text/javascript'>alert('LOGIN FALHADO!')</script>";     
                }               



}

} 
        if(isset($_POST['submit'])) 
        { 
            SignIn(); 
        } 
?>

I'm getting frustrated because I'm about 5 days to change the code and I can not find a solution to this problem, I hope you can help, any help is welcome and thank you very much, thank you very much.