Ma session_start ne fonctionne pas

<?php
//Demarrage de la SESSION
session_start();
//connexion à la base de donnees
  require 'dbconnectM.php';

      error_reporting(E_ALL);
   ini_set('display_errors', TRUE);
   ini_set('display_startup_errors', TRUE);

   if(isset($_POST['formconnex']))
   {
    $pseudoconnect = htmlspecialchars($_POST['pseudo']);
    $mdpconnect = sha1($_POST['pass']);
    if(!empty($pseudoconnect) AND !empty($mdpconnect))
    {
     $requser = $bdd->prepare('SELECT * FROM membres WHERE pseudo = ? AND pass = ?');
     $requser->execute(array($pseudoconnect, $mdpconnect));
     $userexist = $requser->rowCount();
     $user = $requser->fetch();
     if($userexist == 1)
     {
      $reqconfirme = $bdd->prepare("SELECT * FROM membres WHERE pseudo = ? AND confirmekey = ? AND confirmer = ? ");
      $reqconfirme->execute(array($user['pseudo'],$user['confirmekey'],$user['confirmer']));
      $confirme = $reqconfirme->fetch();
      if($confirme['confirmer'] == 1)
      {
       
       $_SESSION['id'] = $user['id'];
       $_SESSION['pseudo'] = $user['pseudo'];
       
       header('Location:userprofil.php?id=' .$_SESSION['id']);
      }else{
       $err = "Veuillez confirmer votre compte ";
      }

     }
     else
     {
      $err = "Mauvais identifiant ou mot de passe";
     }
    }
    else
    {
     $err = "Tous les champs doivent être complétes ";
    }

   }
?>
<div class="pagemenu"> 
 <div class="header">
 <div class="page_titre">
 <h1>Sitename</h1>

<?php

   error_reporting(E_ALL);
   ini_set('display_errors', TRUE);
   ini_set('display_starup_errors', TRUE);

   require_once 'dbconnectM.php';

   //------------- functions ---------------/
   //functions
   //------------------------------/

   /*Fair une requete SELECT et retoune 1 ligne */

   function querySelectOneRow($sql,$datas=NULL){
    global $bdd;

    $result = NULL;

    try{
     $req = $bdd->prepare($sql);
     $req->execute($datas);
     $result = $req->fetch();
    }catch(Exception $e){
     echo 'Error : ' .$e->getMessage();
     echo "Les datas";
     print_r($datas);
    }
    return $result;
   }

   /* Recuper les info d'un user en fonction de son ID */

   function getUserInfosByID($id){
    $sql = "SELECT * FROM membres WHERE id = ?";
    $datas = array($id);
    return querySelectOneRow($sql,$datas);
   }

   
   $id = !empty($_SESSION['id']) ? $_SESSION['id'] : NULL;

    if($id){
     $result = getUserInfosByID($id);
     if(!empty($result)){
      echo '<span class="Userpseudo">'.$result['pseudo'].'</span><a class="Userprofil" href="userprofil.php?id='.$id.'"> Mon profil</a>';

      echo '<span class="userdeconnect" id="userdeconnect"><a href="deconnection.php">Se deconnecter</a></sapn>';
     }
     
    }else{
      echo '<div class="logine">
       <b><a href="inscription.php">Inscription</a></b>
         </div>';

     echo '<div class="Divlogin">
       <b><a href="connecter.php">Connexion</a></b>

       <div class="login">
        <form method="POST" action="">
         <tr>
          <td>
           <label for="pseudo">Pseudo :</label>
          </td>
          
          <td>
           <input type="text" name="pseudo" id="pseudo" placeholder="pseudo" />
          </td>
         </tr>

            <tr>
            
          <td>
           <label for="mdp">Mot de passe :</label>
          </td>
          
          <td >
           <input id="mdp" type="password" name="pass" placeholder="mot de passe" />
          </td>
         </tr>

         </table>
         <hr>
         <input type="submit" name="formconnex" value="se connecter">
        </form>
        
       </div>
      
      </div>';

    }



   
  ?>

</div>


      <nav id=sidenave class="sidenav">
       <a href="javascript: void(0)" class="closebtn" onclick="closeNav()">×</a>
       <ul class="menu_drow">
                        <li class="navi"><i class="fa fa-home" aria-hidden="true" id="awesome"></i><a href="datamee.php">site</a></li>
        <li class="navi"><i class="fa fa-gamepad" aria-hidden="true" id="awesome"></i><a href="a2jeux.php">site</a>
         
         <ul class="apps_drow">
          <li><i class="fa fa-android" aria-hidden="true" id="awesome"></i><a href="#">site</a></li>
          <li><i class="fa fa-apple" aria-hidden="true" id="awesome"></i><a href="#">site</a></li>
          <li><i class="fa fa-windows" aria-hidden="true" id="awesome"></i><a href="#">site</a></li>
         </ul>
         
        </li>
        <li class="navi"><i class="fa fa-rocket" aria-hidden="true" id="awesome"></i><a href="a3apps.php">site</a>
         <ul class="apps_drow">
          <li><i class="fa fa-android" aria-hidden="true" id="awesome"></i><a href="#">site</a></li>
          <li><i class="fa fa-apple" aria-hidden="true" id="awesome"></i><a href="#">site</a></li>
          <li><i class="fa fa-windows" aria-hidden="true" id="awesome"></i><a href="#">site</a></li>
         </ul>
        
        </li>
        
        
        <li class="navi"><i class="fa fa-mobile" aria-hidden="true" id="awesome"></i><a href="a4phone.php">Phone</a></li>

        <li class="navE"><a href="#">site</a></li>
        <li class="navE"><a href="#">site</a></li>
        <li class="navE"><a href="#">site</a></li>
        <li class="navE"><a href="#">site</a></li>
        <li class="navE"><a href="#">site</a></li>
        <li class="navE"><a href="#">site</a></li>
       </ul>
      </nav>
   
      <span style="font-size: 30px;cursor: pointer" id="bars" onclick="openNav()"><i class="fa fa-bars" aria-hidden="true"></i></span>
   
      <div id="main">
   
      </div>
      
      
       
       <!-- voici la bare de recherche -->
      <div class="search_">
       <form class="search_q" method="GET" action="resultat_recherche.php">
         <input type="hidden" name="search" value="s">
         <input type="search"  name="g"  placeholder="Recherche" /><button  name="submit" onclick="valid(this, 'resutats-search');" >Go</button>
         
  
       </form>
      </div>
       <?php
        if(isset($msg)){
         echo '<b style="color:darkred">' .$msg. '</b>';
        }
       ?>
  
  
      
   
     <!-- Le Menu de deroule telephone-->
      <div id="menu">
       <ul>
        <li id="menue"><a href="#">site</a></li>
        <li id="menuee"><a href="#">site</a>
         <ul>
          <li><a href="#">site</a></li>
          <li><a href="#">site</a></li>
          <li><a href="#">site</a></li>
          <li><a href="#">site</a></li>
          <li><a href="#">site</a></li>
         </ul>
        </li>
        <li><div id="btnsearh"></div><button id="btsh" onclick="srhBtn()">search</button></li>
       </ul>
      </div> 
  
     </div>   
     </div>

<?php
include_once "codemenu.php";

//connextion
require_once 'dbconnectM.php';

if(isset($_GET['section'])){
 $section = htmlspecialchars($_GET['section']);
 
}
else{
 $section = "";
}

if(isset($_POST['recup_submit'],$_POST['recup_mail'])){
 if(!empty($_POST['recup_mail'])){
  $recup_mail = htmlspecialchars($_POST['recup_mail']);
  if(filter_var($recup_mail,FILTER_VALIDATE_EMAIL)){
   $mailexist = $bdd->prepare('SELECT id, pseudo FROM membres WHERE email = ? ');
   $mailexist->execute(array($recup_mail));
   $mailexist_count = $mailexist->rowCount();
   if($mailexist_count == 1){
    $pseudo = $mailexist->fetch();
    $pseudo = $pseudo['pseudo'];
    
    $_SESSION['recup_mail'] = $recup_mail;
    
    $recup_code =  "";
    for ($i=0; $i < 8; $i++) { 
     $recup_code .= mt_rand(0,9);
    }
    

    $mail_recup_exist = $bdd->prepare("SELECT id FROM recuperation WHERE email = ?");
    $mail_recup_exist->execute(array($recup_mail));
    $mail_recup_exist = $mail_recup_exist-> rowCount();

    if($mail_recup_exist == 1){
     $recup_insert = $bdd->prepare("UPDATE recuperation SET code = ? WHERE email = ?");
     $recup_insert->execute(array($recup_code,$recup_mail));
    }
    else{ 
     $recup_insert = $bdd->prepare("INSERT INTO recuperation(email,code) VALUES(?,?)");
     $recup_insert->execute(array($recup_mail,$recup_code));
    }
    $header="MIME-Version: 1.0\r\n";
    $header.='From:\'Datamobmee\'<datamobmee12@gmail.com>'."\n";
    $header.='Content-Type:text/html; charset="uft-8"'."\n";
    $header.='Content-Transfer-Encoding: 8bit';

    $message='
    <html>
     <body>
     <font color="#aaa";>
      <div align="center">
       
       blabla de Gmail...
      </div>

     </font>
     </body>
    </html>
       ';

    mail($recup_mail, "Recuperation de mot de passe !", $message, $header);
    header("Location:http://localhost/datamobmee/recup_mdp.php?section=code");

    $errore = '<span id="errr">Votre compts a été bien crée<a href="connecter.php">  Me connecter</a></span><br/><br/>

    <span id="errr1">Un message de confirmation a été envoyé a votre boite e-mail</span> ';

   }
   else{
    $msg_errer = "Cette adresse mail n'est pas enregistrée";
   }
  }
  else{
   $msg_errer = "Adresse mail invalide";
  }
 }
 else{
  $msg_errer = "Veuillez entre votre adresse mail";
 }
}
 
 if(isset($_POST['verif_submit'],$_POST['verif_code'])){
  if(!empty($_POST['verif_code'])){
   $verif_code = htmlspecialchars($_POST['verif_code']);
   $verif_req = $bdd->prepare("SELECT id FROM recuperation WHERE email = ? AND code = ?");
   $verif_req->execute(array($_SESSION['recup_mail'],$verif_code));
   $verif_req = $verif_req->rowCount();
   if($verif_req == 1){
    $del_req = $bdd->prepare("DELETE FROM recuperation WHERE email = ?");
    $del_req->execute(array($_SESSION['recup_mail']));
    header("Location:http://localhost/datamobmee/recup_mdp.php?section=changemdp");
   }
   else{
    $msg_errer = "Code invalide";
   }
  }
  else{
   $msg_errer = "Veuillez entre votre code de verification";
  }
 }
 if(isset($_POST['change_submit'])){
  if(isset($_POST['change_mdp'],$_POST['change_mdpc'])){
   $mdp = htmlspecialchars($_POST['change_mdp']);
   $mdpc = htmlspecialchars($_POST['change_mdpc']);
   if(!empty($mdp) AND !empty($mdpc)){
    if($mdp == $mdpc){
     $mdp = sha1($mdp);
     $ins_mdp = $bdd->prepare('UPDATE membres SET pass = ? WHERE email = ?');
     $ins_mdp->execute(array($mdp,$_SESSION['recup_mail']));
     header("Location:http://localhost/datamobmee/connecter.php");
    }
    else{
     $msg_errer = "Vos deux mot de passes ne correspondent pas";
    }

   }
   else{
    $msg_errer = "Veuillez remplir tous les champs";
   }
  }
  else{
   $msg_errer = "Veuillez remplir tous les champs";
  }
 }
?>


<!DOCTYPE html>
<html>
<head>
 <title>Recuperation de mot de passe</title>
 <meta charset="utf-8">
 <link rel="stylesheet" type="text/css" href="style.css">
</head>
<body>
 <div class="page_principal1">
 <div class="recup">
  
  <?php if($section == 'code') { ?>
  <p>Un code de verifcation a eté envoyer a cette adresse <b><?= $_SESSION['recup_mail'] ?></b> </p>
  <h4>Entrez votre code de verification : </h4>
  
  <form method="post" class="default-form">
   <p>
    <input type="text" name="verif_code" placeholder="Code de verification" size="30">
   </p>
   <p>
    <input type="submit" id="mitsub" name="verif_submit" value="Valide">
   </p>
  </form>
  
  <?php } elseif($section == 'changemdp'){ ?>
  <h4>Nouveau de mot de passe pour : </h4><b><?= $_SESSION['recup_mail'] ?></b>
  <form method="post" class="default-form">
   <p>
    <input type="password" name="change_mdp" placeholder="Nouveau mot de passe" size="30">
   </p>
   <p>
    <input type="password" name="change_mdpc" placeholder="Confirmation du mot de passe" size="30">
   </p>
   <p>
    <input type="submit" id="mitsub" name="change_submit" value="Valide">
   </p>
  </form>

  <?php } else { ?>
  <h2>Recuperation de mot de passe</h2>
  <form method="post" class="default-form">
   <p>
    <input type="email" name="recup_mail" placeholder="Votre adresse mail" size="30">
   </p>
   <p>
    <input type="submit" id="mitsub" name="recup_submit" value="Valide">
   </p>
  </form>

  <?php } ?>

  <?php if(isset($msg_errer)) { echo '<font color="red">'.$msg_errer.'</font>';} ?>
 </div>



</div>
</body>
</html>