PDO Uncaught Error: Call to a member function fetch() on bool

Uncaught Error: Call to a member function fetch() on bool

<?php

try {
    $bdd= new PDO('mysql:host=localhost;bdname=isj;charset=utf8','root','');     
}catch(Exception $e){
  die('erreur:'.$e->getMessage());
}

$query = $bdd -> query ('SELECT * FROM etudiant');
 while ($donnees = $query->fetch()) {
  echo $donnees['nom'];
 }   

?>

EDIT : Ajout des balises de code et du "bonjour"