It is possible to means to access a MySQL database with C# when exterior access isn't enabled and that i don't have any method to enable it? Some kind of PHP interface or something like that like this maybe? Thanks ahead of time.

You can write your personal protocol on the top of HTTP, (or on the top of Cleaning soap, on the top of HTTP) but you have to make sure that you are not undermining the safety in so doing....

<?php

$shared_secret = 'shhhh_s3cr3t!';
$qry=$_GET['qry'];
$remote_ip=_SERVER["REMOTE_ADDR"];
if (sha1($shared_secret . $qry , $remote_ip)!=$_GET['auth']) {
         header("HTTP/1.1 401 Unauthorized");
         print "not authorized!";
         exit;
} else {
   $dbh=mysql_connect($db_host, $db_user, $db_pass);
   if ($dbh===false) error_reply();
   $r=mysql_query($_GET['qry'], $dbh);
   if ($r===false) error_reply();
   $result=array();
   while ($result[]=mysql_fetch_assoc($r));
   print serialize($result);
   exit;
}

function error_reply()
{
   header("HTTP/1.1 503 Internal Server Error");
   print mysql_error();
}

Use of a MySQL DB is governed by if the DB is set up to pay attention on the port from remote IP addresses, and if the network enables traffic in on that port. Both database and also the firewall/network need setting up. Unless of course they are both set up to permit exterior access, you will not have the ability to achieve the DB remotely with anything.

If they are setup and set up properly, then you definitely should have the ability to access the DB remotely in some way utilizing a client library. I'm not sure whether C# features its own limitations on hooking up to some remote DB, whether it does, then yes, you should find a different way to connect that may be wrapped by C#.