I got access denied and link to server could not established error

Question

I got access denied and link to server could not be established error. This is my code, can you explain to me what is wrong?

<?php

session_start ();
include("includes/db.php");

if(isset($_POST['login'])) {
    $email = mysql_real_escape_string($_POST['email']);
    $pass = mysql_real_escape_string($_POST['pass']);
    $sel_user = "select * from admins where user_email='$email' AND user_pass='$pass'";
    $run_user = mysqli_query($con, $sel_user);
    $check_user = mysqli_num_rows($run_user);
}