Need help enabling session_start variable.....it does not seem to be working properly??

I have a login page that should check to see if the user is authenticatedor logged in when the user clicks 'My Account' button but it is just reloading the login page even though in the top left corner of the page it shows user is logged in.  

What should happen is it check of there is a session variable and if so take that user to his account info.  if not it should load the login.php page

Can you look at the code to see whats going on...dont quiet understand what going on in this login form.

Thanks

<?php
require_once('Connections/myconn.php');
// *** Validate request to login to this site.
unset($_SESSION['MM_Username']);
unset($_SESSION['MM_UserGroup']);
unset($_SESSION['memberId']);
session_unregister('MM_Username');
session_unregister('MM_UserGroup');
session_unregister('memberId');

$loginFormAction = $_SERVER['PHP_SELF'];
if (isset($accesscheck)) {
  session_register('PrevUrl');
  $_SESSION['PrevUrl'] = $accesscheck;
}

if (isset($_POST['username'])) {
  $loginUsername=$_POST['username'];
  $password=$_POST['password'];
  $MM_fldUserAuthorization = "login_check.php";
  $MM_redirectLoginSuccess = "memberindex.php";
  $MM_redirectLoginFailed = "login.php";
  $MM_redirecttoReferrer = false;
  mysql_select_db($database_myconn, $myconn);
 
  $LoginRS__query=sprintf("SELECT id,email,name, password FROM members WHERE email='%s' AND password='%s' and active = 'Yes' ",
    get_magic_quotes_gpc() ? $loginUsername : addslashes($loginUsername), get_magic_quotes_gpc() ? $password : addslashes($password));
   
  $LoginRS = mysql_query($LoginRS__query, $myconn) or die(mysql_error());
  $loginFoundUser = mysql_num_rows($LoginRS);
  if ($loginFoundUser) {
        //admin type
     $loginStrGroup = "MEMBER";
   
      $array = mysql_fetch_assoc($LoginRS);
      //$GLOBALS['memberID'] = $array['id'];
      //$GLOBALS['memberName'] = $array['name'];
      
    //declare two session variables and assign them
   // $GLOBALS['MM_Username'] = $loginUsername;
   // $GLOBALS['MM_UserGroup'] = $loginStrGroup;      
        
    //register the session variables
    session_register("MM_Username");
      $_SESSION['MM_Username'] = $loginUsername;
    session_register("MM_UserGroup");
      $_SESSION['MM_UserGroup'] = $loginStrGroup;
      session_register("memberID");
      $_SESSION['memberID'] = $array['id'];
      session_register("memberName");
      $_SESSION['memberName'] = $array['name'];

      mysql_query('update members set last_login = NOW() where id = '.$array['id'],$myconn) or die(mysql_error());
    if (isset($_SESSION['PrevUrl']) && false) {
      $MM_redirectLoginSuccess = $_SESSION['PrevUrl'];      
    }
    header("Location: " . $MM_redirectLoginSuccess );
  }
  else {
    header("Location: ". $MM_redirectLoginFailed );
  }
}
include('header.php');
?>
<FORM ACTION="<?php echo $loginFormAction; ?>" METHOD="POST" >