Problemas com mysqli

Alguem me ajuda não estou conseguindo resolver...

Olha os erros:

Success: A proper connection to MySQL was made! The my_db database is great. Host information: localhost via TCP/IP
Warning: mysqli_query(): Couldn't fetch mysqli in C:\xampp\htdocs\ranking.php on line 17

Warning: mysqli_fetch_array() expects parameter 1 to be mysqli_result, null given in C:\xampp\htdocs\ranking.php on line 18

Warning: mysqli_query(): Couldn't fetch mysqli in C:\xampp\htdocs\ranking.php on line 104

Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, null given in C:\xampp\htdocs\ranking.php on line 105

Warning: mysqli_query(): Couldn't fetch mysqli in C:\xampp\htdocs\ranking.php on line 111

Warning: mysqli_fetch_array() expects parameter 1 to be mysqli_result, null given in C:\xampp\htdocs\ranking.php on line 112

Notice: Undefined variable: tp in C:\xampp\htdocs\ranking.php on line 276

Warning: mysqli_close(): Couldn't fetch mysqli in C:\xampp\htdocs\ranking.php on line 284

Code da config.php:

<?php
ob_start();
session_start();

$conn = mysqli_connect("localhost", "root", "000", "novadb") or die(mysqli_error());

// Check connection

if (!$conn) {
 die("Connection failed: " . mysql_connect_error());
	//die("conexão falhou.");
}

if (!$conn) {
 echo "Error: Unable to connect to MySQL." . PHP_EOL;
 echo "Debugging errno: " . mysqli_connect_errno() . PHP_EOL;
 echo "Debugging error: " . mysqli_connect_error() . PHP_EOL;
 exit;
}

echo "Success: A proper connection to MySQL was made! The my_db database is great." . PHP_EOL;
echo "Host information: " . mysqli_get_host_info($conn) . PHP_EOL;

mysqli_close($conn);
?>

Página do ranking.php

<?php
include "config.php";

//echo $_SESSION['id_usuario'] . "<br>";
//echo $_SESSION['usuario'];

/* if ($_SESSION['usuario'] == "") {

	echo "É necessário realizar o login. Clique <a href='login.php'>aqui</a> e faça o login.";
	exit;
}

*/

//echo $_SESSION['usuario'];

$id_marca = isset( $_GET["id"] );
$sql = mysqli_query($conn,"select * from tb_marca where id = '$id_marca'");
$rec = mysqli_fetch_array($sql);

$id_categoria = $rec["id_categoria"];

$total_reg = "100"; // número de registros por página

$pagina= isset($_GET['pagina']);

if ($pagina == 1)

{

	$pagina= $_GET['pagina'];
}

if (!$pagina)

{

	$pc = "1";
}

else {

	$pc = $pagina;
}

$inicio = $pc - 1;
$inicio = $inicio * $total_reg;

//echo $_SESSION['usuario'];
?>

<?php include 'layout/metas.php';?>
<?php include 'layout/config_layout.php';?>

<title><?PHP echo "" . $titleindex[0] . " - " . $title[0] . "" ?></title>
<meta name="description" content="<?PHP echo $descriptionindex; ?>" />

<?php include 'layout/header.php';?>

<?php include 'layout/logo.php';?>

<div class="content">
	<table border="0" cellpadding="1" cellspacing="1">
 <tr>
 <td>
 Selecione a Categoria:
 </td>
 <td>
 <select name="cmbcategoria" class="form-control" id="cmbcategoria" onchange="CarregaCidades(this.value)">
 <option value="">Selecione</option>
 <?php
 $sql = mysqli_query($conn,"SELECT * FROM tb_categoria order by categoria");
 while($linha = mysqli_fetch_object($sql))
 {

 $id = $linha->Id;
 $categoria = $linha->categoria;
 ?>
 <option value="<?php echo $id;?>" <?php if ($id == $id_categoria) { echo "SELECTED"; } else { echo ""; }; ?>><?php echo $categoria;?></option>
 <?php
 }
 //mysql_free_result( $resposta );
 //mysql_close($conexao);
 ?>
 </select>
 </td>
 </tr>
	</table>
	<br>
	<div id="cidadeAjax">
 <table border="0" class="table table-striped" cellpadding="3" cellspacing="3" width="100%">
 <tr>
 <td>
 <b>#</b>
 </td>
 <td>
 <b>Marca</b>
 </td>
 <td>
 <b>Avaliação</b>
 </td>
 <td>
 <b>Comentários</b>
 </td>
 </tr>
 <?php

 $sql = mysqli_query($conn,"select count(1) as total_coment, b.id_marca, a.marca, sum(b.avaliacao) as total, a.id_categoria
 from tb_marca a, tb_comentario b where a.id = b.id_marca
 group by b.id_marca, a.marca order by count(1) desc ");
 $num_rows = mysqli_num_rows($sql);

 //echo $num_rows;

 if ($num_rows == 0)
 {
 $quer = mysqli_query($conn,"select a.Id, a.id_categoria, a.marca from tb_marca a, tb_categoria b where a.id_categoria = b.id and a.id_categoria = $id_categoria");
 $rec1 = mysqli_fetch_array($quer);

 $id_marca = $rec1["Id"];
 $id_categoria = $rec1["id_categoria"];
 $marca = $rec1["marca"];
 $total_coment = "0";
 $total_comentarios = "0";

 ?>
 <tr onclick="location.href = 'marca.php?id_marca=<?php echo $id_marca;?>';" style="cursor:pointer;">
 <td>
 <?php echo "1";?>
 </td>
 <td>
 <?php echo $marca;?>
 </td>
 <td>
 <img src="layout/images/star_16x16.png">
 <img src="layout/images/star_16x16.png">
 <img src="layout/images/star_16x16.png">
 <img src="layout/images/star_16x16.png">
 <img src="layout/images/star_16x16.png">
 </td>
 <td>
 <?php echo "0 comentário(s)"; ?>
 </td>
 </tr>
 <?php
 }
 else
 {
 $j = 1;

 /*$sql = mysqli_query($conn,"select count(1) as total_coment, b.id_marca, a.marca, sum(b.avaliacao) as total, a.id_categoria
 from tb_marca a, tb_comentario b where a.id = b.id_marca
 group by b.id_marca, a.marca order by count(1) desc LIMIT $inicio, $quantidade ");*/

 $busca = "select count(1) as total_coment, b.id_marca, a.marca, sum(b.avaliacao) as total, a.id_categoria
 from tb_marca a, tb_comentario b where a.id = b.id_marca
 group by b.id_marca, a.marca order by count(1) desc";

 $limite = mysqli_query($conn,"$busca LIMIT $inicio,$total_reg");
 $todos = mysqli_query($conn,"$busca");

 $tr = mysqli_num_rows($todos); // verifica o número total de registros
 $tp = $tr / $total_reg; // verifica o número total de páginas

 /*$sql = mysqli_query($conn,"select count(1) as total_coment, b.id_marca, a.marca, sum(b.avaliacao) as total, a.id_categoria
 from tb_marca a, tb_comentario b where a.id = b.id_marca
 group by b.id_marca, a.marca order by count(1) desc ");*/

 //$limite = mysqli_query("$sql LIMIT $inicio,$total_reg");
 //$todos = mysqli_query("$sql");

 //$tr = mysqli_num_rows($todos); // verifica o número total de registros
 //$tp = $tr / $total_reg; // verifica o número total de páginas

 while($rec = mysqli_fetch_object($limite))
 {

 $id_marca = $rec->id_marca;
 $id_categoria = $rec->id_categoria;
 $marca = $rec->marca;
 $total_coment = $rec->total_coment;
 $total_comentarios = $rec->total_coment;

 //traz avaliação
 /*
 $query = mysqli_query($conn,"select id_marca FROM tb_comentario where id_marca = $id_marca order by avaliacao desc");
 $objRS = mysqli_fetch_array($query);

 $cod_marca = $objRS["id_marca"];

 echo $cod_marca;
 */

 $sql_ = mysqli_query($conn,"select sum(avaliacao) as total FROM tb_comentario where id_marca = $id_marca");
 $aval = mysqli_fetch_array($sql_);

 $total = $aval["total"];
 //$total = $total/2;

 //echo $total_coment . " - " . $id_marca . "<br>";

 //$sqlco = mysqli_query($conn,"select count(1) as total_coment from tb_comentario where id_marca = $id_marca");
 //$obj = mysqli_fetch_array($sqlco);

 //$total_coment = $obj["total_coment"];

 ?>
 <tr onclick="location.href = 'marca.php?id_marca=<?php echo $id_marca;?>';" style="cursor:pointer;">
 <td>
 <?php echo $j;?>
 </td>
 <td>
 <?php echo $marca;?>
 </td>
 <td>
 <?php
 if ($total_coment >= 5)
 {
 for ($i=1;$i<=5;$i++)
 {
 echo '<img src="layout/images/star1_16x16.png"> ';
 }
 }
 elseif ($total_coment >=3 && $total_coment <5)
 {
 for ($i=1;$i<=$total_coment;$i++)
 {
 echo '<img src="layout/images/star1_16x16.png"> ';
 }

 for ($total_coment;$total_coment<5;$total_coment++)
 {

 echo '<img src="layout/images/star_16x16.png"> ';
 }
 }
 elseif ($total_coment <=2)
 {
 for ($i=1;$i<=$total_coment;$i++)
 {
 echo '<img src="layout/images/star1_16x16.png"> ';
 }

 for ($total_coment;$total_coment<5;$total_coment++)
 {

 echo '<img src="layout/images/star_16x16.png"> ';
 }
 }
 else
 {
 echo '<img src="layout/images/star_16x16.png"> ';
 }
 ?>
 </td>
 <td>
 <?php echo $total_comentarios . " comentários"; ?>
 </td>
 </tr>
 <?php
 $j = $j + 1;
 }
 }
 ?>
 </table>
 <br>
 <?php

// agora vamos criar os botões "Anterior e próximo"

$anterior = $pc -1;
$proximo = $pc +1;
if ($pc>1) {
	echo " <a href='?pagina=$anterior'><- Anterior</a> ";
}

echo "|";
if ($pc<$tp) {
echo " <a href='?pagina=$proximo'>Próxima -></a>";
}
 ?>
</div>
</div>
<?php include 'layout/footer.php';?>

<?php mysqli_close($conn);?>

<script language="javascript">
function CarregaCidades(codEstado)

{

	//alert(codEstado);

	if(codEstado){
 var myAjax = new Ajax.Updater('cidadeAjax','lista_ranking.php?codEstado='+codEstado,
 {
 method : 'get',
 }) ;
	}

}
</script>