login problem

When I try to log in, in order to post I keep getting this message:
Fatal error: Call to undefined function: wp_login() in /www/b/bibbsrevenge/htdocs/wp-admin/auth.php on line 4

Here is my auth.php file:

<?php
require_once(ABSPATH . ‘/wp-config.php’);

if ( (!empty($_COOKIE[‘wordpressuser_’ . $cookiehash]) && !wp_login($_COOKIE[‘wordpressuser_’ . $cookiehash], $_COOKIE[‘wordpresspass_’ . $cookiehash], true))
|| (empty($_COOKIE[‘wordpressuser_’ . $cookiehash])) ) {
header(‘Expires: Wed, 5 Jun 1979 23:41:00 GMT’); // Michel’s birthday
header(‘Last-Modified: ‘ . gmdate(‘D, d M Y H:i:s’) . ‘ GMT’);
header(‘Cache-Control: no-cache, must-revalidate’);
header(‘Pragma: no-cache’);

header(‘Location: ‘ . get_settings(‘siteurl’) . ‘/wp-login.php?redirect_to=’ . urlencode($_SERVER[‘REQUEST_URI’]));
exit();
}

?>

Since I ‘m really not all that good at this stuff,, can anyone offer any help? Thanks in advance. . .