like this

<?php
session_start();
require_once("config.php");
$username = $_POST['username'];
$pass = $_POST['password'];
$cekuser = mysql_query("SELECT * FROM user WHERE username = '$username'");
$jumlah = mysql_num_rows($cekuser);
$hasil = mysql_fetch_array($cekuser);
$h_user=$hasil['username'];
$h_pass=$hasil['password'];
$h_lvl=$hasil['level'];
$h_blok=$hasil['blok'];

if ($h_pass==$pass)//jika hasil password sama
{
 //maka user login
 if($h_user !=$username)//jika hasil username tidak sama
 {
 //user tidak tidak ada
 }
 else if($h_blok==="n")
 {
 //login user sukses
 }
 else if($h_blok==="y")
 {
 //user di blokir
 }

}
else {}//pasword salah

?>