// Файл подключения connection.php
<?php

$servername = "localhost";
$username = "st2014";
$password = "progress";

$connection = "";

try {
    $connection = new PDO("mysql:host=$servername;dbname=st2014", $username, $password);
    $connection->exec('SET NAMES utf8');
} catch (PDOException $e) {
    echo "Connection failed: " . $e->getMessage();
}

?>

// Часть кода которая используется в login.php

$userRequest = $connection->prepare("SELECT username, password FROM t164062_users WHERE username = :username");
$userRequest->bindParam(':username', $POST['username']);
$userRequest->execute();
$user = $userRequest->fetchAll(PDO::FETCH_ASSOC);