Menu dorp down n interage com mysql

<?php

require 'config.php';

$query = mysql_query("SELECT idusuario, nome FROM usuario");

?>

<form onsubmit="return validaForm(this)" id="form2" method="post">

<div class="col-sm-12 col-sm-offset-0 col-md-12 col-md-offset-0 main">

<div class="col-md-12">

<h1 class="page-header">

Administrar Aluno</h1>

</div>

<h3>Dados Pessoais:</h3>

 <div class="row">

 <div class="col-md-6">

<div class="form-group">

<label for="nivel">Nome:</label>

 <select class="form-control" id="nome" name="nome" required="">

 <option value="sl" selected>--Selecione--</option>

<?php while($prod = mysql_fetch_array($query)) { ?>

<option value="<?php echo $prod['idusuario'] ?>"><?php echo $prod['nome'] ?></option>

<?php } ?>

 </select>

 </div>

 </div>

<div class="col-md-6">

<div class="form-group">

Quando abro a pagina as opções ficam em branco.;..