The HOST should not have a newline after it, so you should have

client.print("HOST: ");
client.println(server);

In addition your PHP looks dodgy to me. I'm not very familiar with PHP at all, but I think the &s here are left over from something you have removed, and causing syntax errors - just remove them

if (!empty($n) &&)

(You should find the PHP log (where depends on what OS your server is running on) and I think it would point you straight to this problem. No point trying to debug it blind.)

The HOST should not have a newline after it, so you should have

client.print("HOST: ");
client.println(server);

In addition your PHP looks dodgy to me. I'm not very familiar with PHP at all, but I think the &s here are left over from something you have removed, and causing syntax errors - just remove them

if (!empty($n) &&)

I believe your n parameter is going to be in _GET (not _REQUEST). Also, you should check whether it's there, not just assume it is, so:

if isset ( $_GET["n"] )
{
    $n = $_GET["n"];
    // Do your database stuff here
}

(You should find the PHP log (where depends on what OS your server is running on) and I think it would point you straight to this problem. No point trying to debug it blind.)