php - Session variables not carrying over -

i'm trying write log in script set session variable , redirect user page. session variables displays fine on page it's set, on next page not display @ all. have stripped down home page echo session variable.

login.php:

    session_start();      if(isset($_post['process_login'])){             include('php/db.php');              $query = mysql_query("select users.username, users.password users") or die (mysql_error());             while ($result = mysql_fetch_array($query)){                     if (strtoupper($_post['username']) != $result['username'] || md5($_post['password']) != $result['password']){                              echo "<center><font color=red>incorrect username or password</font><center>";                     }                     else{                             $_session['username'] = $_post['username'];                             #echo $_session['username'];                             #printr ($_session);                             echo "<script> window.location = \"home.php\"; </script>";                     }                     //echo $result['username'];             }     } 

home.php

session_start(); echo $_session['username']; 

the way you've got set should work fine.. code have?