ทำหน้า Login แล้วตั้ง Header("location:?p=index.php") มันไม่ไปอ่ะครับ

ทำหน้า Login แล้วตั้ง Header("location:?p=index.php") มันไม่ไปหน้า index.php อ่ะครับ
ตัวอย่างโค้ดครับ
<?
    ob_start();
    include("config.php");
?>
<meta http-equiv="Content-Type" content="text/html; charset=windows-874" />
<script  language="javascript" type="text/javascript">
      function checkField() {
                 missinginfo = "";
             if (document.form1.UserName.value == "") {
                 missinginfo += "\n - Username";
                 }
                if (document.form1.PassWord.value == "") {
                     missinginfo += "\n - Password";
                  }
if (missinginfo != "") {
                      missinginfo = " ------\n" + "ท่านกรอกข้อมูลไม่ถูกต้องในช่องต่อไปนี้:\n" + missinginfo +
                       "\n-----" +   "\nกรุณากลับไปกรอกอีกครั้ง";
                        alert(missinginfo);
                         return false;
                    }
                     else
                         return true;
                }
</script>
<?php

if ($_POST[Login])
{
    header("location:?p=index.php");
    $CK_Q = mysql_query ("SELECT * FROM emp WHERE
    User_id = '". $_POST[User_id] ."'
    AND Password = '" . $_POST[Password] . "' " );
    if (mysql_num_rows ($CK_Q))
    {
        $CK= mysql_fetch_array ($CK_Q);
        $_SESSION[User_id] = $CK[User_id];
        $_SESSION[Password] = $CK[Password];
        $_SESSION[user_status] = $CK[user_status];
        header("location:?p=index.php");
        exit ();
        } else {
    echo "<script>alert('ID หรือ รหัสผ่านไม่ถูกต้อง')</script>";
        }
    }
    ob_end_flush();
?>
<div align="center"><img src="ITD Logo.png" width="679" height="163" /><br />
</div>
<form action="" method="post" name="form1" id="form1" onsubmit="return checkField();">
<table width="200" border="0" align="center" cellpadding="3" cellspacing="0">
  <tr>
    <td><strong>เข้าสู่ระบบ</strong></td>
  </tr>
<tr>
    <td><input name="User_id" type="text" maxlength="5" placeholder="UserName" id="User_id"/></td>
  </tr>
<tr>
    <td><input name="Password" type="password" maxlength="10" placeholder="PassWord" id="Password"/></td>
  </tr>
<tr>
    <td><input name="Login" type="submit" value="Login" id="Login" /></td>
  </tr>
</table>

</form>