php - How to get ob_start() working correctly -

im getting error states:

warning: cannot modify header information - headers sent (output started @ /home/content/21/10941021/html/index.php:4) in /home/content/21/10941021/html/register.php on line 66

im thinking need put ob_start() buffering working correctly can't down. codes problems include:

<div class="lower-body"> <div class="left-lower">create account</div> <div id="account-first"> <?php ob_start(); if (isset($_get['success']) && empty($_get['success'])){     echo 'you\'ve been registered successfully!';     echo 'please check email , activate account!';  }else {  if(empty($_post) === false && empty($errors) === true){     $register_data = array(         'firstname' => $_post['firstname'],         'lastname'  => $_post['lastname'],         'username'  => $_post['username'],         'password'  => $_post['password'],         'email'     => $_post['email'],         'zipcode'   => $_post['zipcode']         );      register_user($register_data);     header('location: register.php?sucess');     exit(); } else if(empty($errors) === false){     echo output_errors($errors);     } } ob_end_flush();?> 

and line 4 this:

<?php ob_start(); include 'includes/overall/head.php'; ?> 

any ideas? lot!

header('location: register.php?sucess'); should before output echo

edit 1: use ob_start(); @ start of php code , ob_end_flush(); @ end, should solve problem.

edit 2: use this

<?php ob_start(); ?> <div class="lower-body"> <div class="left-lower">create account</div> <div id="account-first"> <?php ... ... ob_end_flush(); ?>