Tidak biasa update dan insert database..

ketika di klik simpan pada webnya, tidak tidak terjadi apa-apa misalnya, seperti pesan eror ataupun pesan sukses

<?php

  if(isset($_POST['Simpan'])){
        if($aksi=='edit'){
                if(empty($_POST['password'])){
                  $password   = $_POST['pwd'];
                }else{
                  $password   = $_POST['password'];
                }
            $sql_query = mysql_query("UPDATE user SET username='".htmlentities(trim($_POST['username']))."', password='".htmlentities(trim(md5($password)))."'WHERE id_user='".$_POST['id_user']."'");
         }else{
             $sql_query = mysql_query("INSERT INTO user (username,password) VALUES ('".htmlentities(trim($_POST['username']))."','".htmlentities(trim(md5($_POST['password'])))."')") or die(mysql_error());
         }
  }

  if($aksi=='hapus' && isset($id)){
     $sql_query   = mysql_query("DELETE FROM user WHERE id_user='".$id."'");
  }

  if($aksi=='edit' && isset($id)){
      $sql_display    = mysql_query("SELECT *FROM user WHERE id_user='".$id."'");
      $row_display    = mysql_fetch_assoc($sql_display);
  //    $kredit_tanggal   = $row_display['kredit_tanggal'];
      $id_user      = $row_display['id_user'];
      $hidden         = "hidden";
  }

  if($aksi=='hapus' && isset($sql_query)){
      echo "<script>alert('Delete Succesfully!');window.location='index.php?mod=pembeli'</script>";
  }elseif($sql_query){
      $respond = "<div class='respond'>Update/Insert Successfully</div>";
  }