کار نکردن سیشن لاگین

<?php
mysql_coect("localhost","root","")or die(mysql_error());
mysql_select_db("mehr")or die(mysql_error());
$r=mysql_query("select * from login where useame='".$_POST['useame']."' and password='".$_POST['password']."'");
if(mysql_num_rows($r)>0){
session_start();
$_SESSION['useame']=$_POST['useame'];
$_SESSION['password']=$_POST['password'];
header("location:admin.php");
}
else echo 'ناموفق';
?>