How to fix HTTP 500 Error during Form Submission?

Question

I created a form with the following fields I am getting a HTTP ERROR 500 message when I hit SUBMIT button on my form. I have created the database as a MySQL database with 4 fields. My PHP code looks like below.

<?php
$yname = $_POST['yname'];
$pname = $_POST['pname'];
$details = $_POST['details'];
$links = $_POST['links'];
if (!empty($yname) || !empty($pname) || !empty($details) || !empty($links)) {
$host = "localhost";
$dbUsername = "u172756077_admin";
$dbPassword = "";
$dbname = "u172756077_Form";
$conn = new mysqli($host, $username, $dbPassword, $dbname);
if (mysqli_connect_error()) {
    die('Connect Error('. mysqli_connect_errno().')'.mysqli_cnnect_error());
} 
else {
    $SELECT = "SELECT pname From form Where pname = ? Limit 1";
    $INSERT = "INSERT Into form (yname, pname, details, links) values(?, ?, ?, ?)";
    $stmt = $conn->prepare($SELECT);
    $stmt->bind_param("s", $pname);
    $stmt->execute();
    $stmt->bind_result($pname);
    $stmt->store_result();
    $stmt->fetch();
    $rnum = $stmt->num_rows;
    if ($rnum == 0) {
        $stmt->close();
        $stmt = $conn->prepare($Insert);
        $stmt->bind_param("ssss",$yname, $pname, $details, $links);
        if ($stmt->execute()) {
            echo "New record inserted sucessfully.";
        }
        else {
            echo $stmt->error;
        }
    }
    else {
        echo "Someone already registers using this email.";
    }
    $stmt->close();
        $conn->close();
    }
}
  else {
    echo "All fields are required.";
    die();
}
  else {
    echo "Submit button is not set.";
}
?>