If your server cannot establish a connection with a webpage, you can check where is the problem with a code like the following:
<?php
$link = mysqli_connect("localhost", "user", "psw", "dbname");
/* check connection */
if (mysqli_connect_errno()) {
printf("Connect failed: %s\n", mysqli_connect_error());
exit();
}
if (!mysqli_query($link, "SET a=1")) {
printf("Error message: %s\n", mysqli_error($link));
}
/* close connection */
mysqli_close($link);
?>