code connect เข้าสู่ระบบไม่ได้ค้ะ ระบบบอกว่า Username and Password Incorrect

$strSQL = "SELECT * FROM user WHERE username = '".mysql_real_escape_string($_POST['username'])."' and password = '".mysql_real_escape_string($_POST['password'])."'";

echo $strSQL;

<form action="chk.php" method="post">
<fieldset style="width:35%; border-color:#000;"><legend align="center"><font color="#FF0000"><b>เข้าสู่ระบบ</b></font></legend><br /><br />
<table align="center">
<tr>
	<td align="right"><b>ชื่อผู้ใช้งาน :</b></td>
	<td align="left"><input type="text" id="username" name="username"  style="height:35px; font-size:18px"/></td>
</tr>
<tr><td></td></tr>
<tr><td></td></tr>
<tr>
	<td align="right"><b>รหัสผ่าน :</b></td>
	<td align="left"><input type="text" id="password" name="password" style="height:35px; font-size:18px"/></td>
</tr>

<tr>
    <td colspan="2" align="center">
    <input name="Submit" type="submit" value="เข้าสู่ระบบ" class="button" style="font-size:14px; font-weight:800">
    </td>
</tr>

</table>
</fieldset>
</form>

<?
	session_start();
	mysql_connect("localhost","root","1234");
	mysql_select_db("motor");
	$username=mysql_real_escape_string($_POST['username']);
	$password=mysql_real_escape_string($_POST['password']);
	$strSQL = "SELECT * FROM user WHERE username = '".$username."' and password = '".$password."'";
	$objQuery = mysql_query($strSQL) or die (mysql_error());
	$objResult = mysql_fetch_array($objQuery);
	$num_rows=mysql_num_rows($objQuery);
	if($num_rows == 0)
	{
			echo "Username and Password Incorrect!";
	}
	else
	{
			$_SESSION["user_id"] = $objResult["user_id"];
			$_SESSION["user_type"] = $objResult["user_type"];

			session_write_close();
			
			if($objResult["user_type"] == "1")
			{
				header("location:index_admin.php");
			}
			else if($objResult["user_type"] == "2")
			{
				header("location:index_store.php");
			}
			else if($objResult["user_type"] == "3")
			{
				header("location:index_purchase.php");
			}
			else
			{
				header("location:index_spare.php");
			}
	}
	mysql_close();
?>