php5.5用PDO连接sql-server2008R2无法连接

$dbName = "sqlsrv:Server=localhost;Database=YTHIIS";
用localhost可以连接，用计算机名也可以连接（但只限本地）

$dbName = "sqlsrv:Server=127.0.0.1;Database=YTHIIS";
用127.0.0.1无法连接，192.168.2.118局域网IP也无法连接，局域网计算机名也无法连接。

 <?php
 try {
    $dbName = "sqlsrv:Server=localhost;Database=YTHIIS";
    $dbUser = "sa";
    $dbPassword = "sa123";
    $db = new PDO($dbName, $dbUser, $dbPassword);
    if ($db) {
        echo "<b style='color: green'>Database connect succeed.</b><br />";
    }
}
catch (PDOException $e) {
    $content = iconv("UTF-8","gbk",$e->getMessage());
    echo   $content . "<br />";
    echo "Hello World!";
}

 ?>