function validate_login($email , $password){
        global $_config;
        if(empty($email) or empty($password)){
            return false;
        }

        //Now perform validation here
        //$email = mysql_real_escape_string($email);
        //$password = mysql_real_escape_string($password);

        $query_obj = new execute_query();
        $where = 'email="'.$email.'" and password = md5("'.$password.'")';
        $result = $query_obj->select_query(array('*') , 'user' , $where);

        $user = array();

        if($result->num_rows > 0){

            $user = array();
            while($row = $result->fetch_assoc()) {
                $user = $row;
                $user['is_logged'] = true;
            }

            session_start();
            $_SESSION['user'] = $user;
            $url  = $_config['site_url'].'dashboard.php';
            //header('Location :'.$url);die;
            header("Location: ".$url);
        }
        return false;
    }

<?php
session_start();
//echo "<pre>";print_r($_SESSION['user']);die;
if(!isset($_SESSION['user'])){
    $url  = $_config['site_url'].'login.php';
    //header('Location :'.$url);die;
    header("Location: ".$url);
} ?>