Error with connection between php and mysql

Question

first of all sorry for my english, I have a problem with my project I skip the following error when trying to connect with mysql from the index

Parse error: syntax error, unexpected 'self' (T_STRING) in C:\xampp\htdocs\app\Conexion.inc.php on line 11

How do I solve this error? I already made an adaptation to the following code http://us.php.net/manual/en/pdo.construct.php and it works to me but it is useless for my project I need to correct the one that already I put up.

I leave the files of my project thanks beforehand

Conexion.inc.php

<?php

class Conexion {

    private static $conexion;

    public static function abrir_conexion() {
        if (!isset(self::$conexion)) {
            try {
                include_once 'config.inc.php'
                self::$conexion = new PDO("mysql:host=$nombre_servidor; dbname=$nombre_base_datos", $nombre_usuario, $password);
                self::$conexion -> setAtribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
                self::$conexion -> exec("SET CHARACTER SET uft8");

                print "Conexion Abierta";
            } catch (PDOException $ex) {
                print "ERROR: " . $ex -> getMessage() . "<br>";
                die();
            }
        }
    }

    public static function cerrar_conexion() {
        if (isset(self::$conexion)) {
            self::$conexion = null;
            print "CONEXION CERRADA";
        }
    }

    public static function obtener_conexion() {
        return self::$conexion;
    }
}

index.php here is just a small code to check the connection

<?php
include_once 'app/Conexion.inc.php';

Conexion :: abrir_conexion();
Conexion :: cerrar_conexion();
?>

config.inc.php

<?php

$nombre_servidor = '127.0.0.1';
$nombre_usuario = 'root';
$password = '';
$nombre_base_datos = 'blog';