probleme ouverture session (header)

Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at /homepages/12/d311644604/htdocs/payetonju/www/includes/fonctions-systemes.php:1) in /homepages/12/d311644604/htdocs/payetonju/www/connexion.php on line 64

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /homepages/12/d311644604/htdocs/payetonju/www/includes/fonctions-systemes.php:1) in /homepages/12/d311644604/htdocs/payetonju/www/connexion.php on line 64

 <?php

<?php

<?php
include_once("fonctions-systemes.php");
if(isset($_POST['login']) && isset($_POST['password']))
{
  if($_POST['login'] == "" )
  {
    $erreurs['general'] = "<font color='red' size='1'>T'as oubli&eacute; d'entrer ton login</font>";
  }
  elseif($_POST['password'] == "" )
  {
    $erreurs['general'] = "<font color='red' size='1'>T'as oubli&eacute; d'entrer ton mot de passe</font>";
  }
  elseif($_POST['login'] != "" && $_POST['password'] != "" ) 
  {
    
    
    $Login = $_POST['login'];
    $Pwd = $_POST['password'];
    $Conn = mysql_connect($host,$user,$pwd);
    $db= mysql_select_db($bdd, $Conn); 
    $sql = "select NOM,PRENOM,EMAIL,PASSWORD,LOGIN,VALIDE from utilisateurs where LOGIN = '".$Login."' and PASSWORD = '".$Pwd."' ";
	
    $res = mysql_query($sql);

    if(mysql_fetch_assoc($res))
    {
      // $trouve le nombre de resultats d'une requete de lecture nb = mysql_num_rows($res);
      // 0 est le numéro de la ligne à récupérer
      $prenom = mysql_result($res,0,"PRENOM");
      $pass = mysql_result($res,0,"PASSWORD");
      $login = mysql_result($res,0,"LOGIN");
      $Valide = mysql_result($res,0,"VALIDE");
      mysql_close($Conn);
      if($Valide == 0 )
      {
        $erreurs['general'] = "<font color='red' size='1'>Tu n'as pas encore valid&eacute; ton compte !</font>";
      }
      else
      {
        if( $Login == $login && $Pwd == $pass )
        {
          // si le pass envoyé ET le login sont egale a ceux de la base ALORS connexion
          session_start();
          $_SESSION['langage'] = 'PHP 5'; 
          $_SESSION['login'] = $Login;
          $_SESSION['prenom'] = $prenom;
          //header("location:/index.php");
          //exit();
          echo " <script language=\"Javascript\">var t=setTimeout(\"document.location.replace(\'index.php\')\", 0);</script>";
        }
        else
        {
          $erreurs['general'] = "<font color='red' size='1'>Mauvais login ou mot de passe</font>";
         /* echo "log envoyé : [".$Login."]<br>";
          echo "log base : [".$login."]<br>";
          echo "pass envoyé : [".$Pwd."]<br>";
          echo "pass base : [".$pass."]<br>"; */
        }
      }
    }
    else
    {
      $erreurs['general'] = "<font color='red' size='1'>Mauvais login ou mot de passe !</font>";
    }
  }
  else
  {
    $erreurs['general'] = "<font size=2 color='red'><b>Donn&eacute;es incorectes</b></font>";
  }
}

if(isset($erreurs))
{
  include("index.php");
}

?>

<?php
    $Login = $_POST['login'];
    $Pwd = $_POST['password'];
?>

<?php
if($TagSys != 1)
{
  $TagSys = 1;

  session_start();

  function Random($car, $Ambiguite = NULL ) 
  {
    $string = "";
    if( $Ambiguite == NULL )
    {
      $chaine = "0123456789abcdefghijklmnopqrstuvwxyz";
    }
    else
    {
      // élimine les chiffres 0 et 1 ainsi que les lettres O et I
  
      $chaine = "23456789abcdefghjklmnpqrstuvwxyz";
    }
    srand((double)microtime()*1000000);
    for($i=0; $i<$car; $i++) 
    {
      $string .= $chaine[rand()%strlen($chaine)];
    }
    return $string;
  }

  function LitFichier( $NomFichier )
  {
    $Contenu = "";

    $Fichier = fopen( $NomFichier, "r" );
    if( $Fichier != false )
    {
      while( !feof( $Fichier ) )
      {
        $Contenu .= fread( $Fichier, 1024 );
      }
      fclose( $Fichier );
    }
    else
    {
      echo "Fichier:$NomFichier, introuvable<br />";
    }
    return $Contenu;
  }

  function makeguid( $class )
  {
    if( $class == "NULL" ) return "00000000-0000-0000-0000-000000000000";
    $baseuuid = substr( $class.random(32), 0, 32);
    $struuid = md5( $baseuuid );
    return strtoupper(substr( $struuid, 0, 8 )."-".substr( $struuid, 8, 4 )."-".substr( $struuid, 12, 4 )."-".substr( $struuid, 16, 4 )."-".substr( $struuid, 20, 12 ));
  }
}
?>

$Login = $_POST['login'];
$Pwd = $_POST['password'];

$_POST['login'] = $Login;
$_POST['password'] = $Pwd;