Connexion d'un administrateur ou d'un utilisa

j ai toujours cette message d'erreur 'Warning: Cannot modify header information - headers already sent by (output started at c:\program files\easyphp1-8\www\bci\tete.php:6) in c:\program files\easyphp1-8\www\bci\connexion.php on line 55'
Merci d'avoir m'aider
Vous trouvez si dessus le code
<?php include("tete.php"); ?>
<div class="art-content">
<div class="art-Post">
<div class="art-Post-body">
<div class="art-Post-inner">
<br><br>
<p class="title">Connexion</p>
<h4>Cette page vous permet de vous connecter en tant que un opérateur ou un administrateur</h4>
<form action="index.php" method="post" >
<?php if(isset($_COOKIE["PSEUDO"])){
?>
<input type="button" name="deco" value="deconnexion" onClick="location.href='deconnexion.php'" class="bot">
<?php } ?><br>
Pseudo: <input type="text" name="pseudo" /><br /><br />
Mot de passe:<input type="password" name="pwd" value=""/><br /><br />
<input type="submit" value="Se connecter" class="bot"><br />

<br><br><br>
<?php
if (isset($_POST['pseudo']) AND isset($_POST['pwd'])){
if ($_POST['pseudo'] != NULL AND $_POST['pwd'] != NULL){
$pseudo = htmlentities ($_POST['pseudo']);
$pwd = htmlentities ($_POST['pwd']);
mysql_connect("localhost", "root", " ") ;
mysql_select_db("stage");
$res1 = mysql_query("select * from operateurs;");
while($tab = mysql_fetch_array($res1) AND ($pseudo != $tab['pseudo']) AND ($pwd != $tab['pwd']));
if(($pseudo == $tab['pseudo']) AND ($pwd == $tab['pwd'])){
setcookie("PSEUDO", $tab["pseudo"], time()+3600, "/");
header('Location: index.php');
}
else ?> <script type="text/javascript"> alert( 'le pseudo ou/et mot de passe n\'existe(s) pas');
</script>
<?php }
}
?>

<?php if(isset($_COOKIE["ADMIN"])){
?>

<?php } ?>
<br><br><br><br>
<?php if(isset($_COOKIE["ADMIN"])){
?>

</form>
<br><br><br>
<?php
if (isset($_POST['pwd'])){
if ($_POST['pwd'] != NULL){
$pwd = $_POST['pwd'];
mysql_connect("localhost", "root", "");
mysql_select_db("stage");
$res1 = mysql_query("select * from admin;");
while($tab = mysql_fetch_array($res1))
if($pwd == $tab['pwd']){
setcookie("ADMIN", $tab["pwd"], time()+3600, "/");
header("Location: index.php");
}
else
echo 'le mot de passe n\'existe pas';
}
}
?> <?php } ?> <br><br><br>
<br><br><br><br><br><br>
<br>

<div class="cleared"></div>
</div>
</div>
</div>
<?php include("bas.php");?>