Installation problem:relative path

I’ ve installed wordpress. Instalation message was ok, but then nothing was displayed when loading index.php or b2login.php. I`ve modified the config file adding “$abspath = ‘../wordpress/’;” at the bottom of it, and then there was the main page . But now when I try to log in, entering username and password a blank page is shown.
Can anybody help me ?. Thanks .
Here the end lines of my b2config.php file:
$relpath = ”;
$url = explode(‘/’, $siteurl);
for ($i = 3; $i < count($url); $i++) {
$relpath .= ‘/’. $url[$i];
}
$abspath = getenv(‘DOCUMENT_ROOT’) . $relpath . ‘/’;
$b2inc = “/$b2inc”;
$pathserver = &$siteurl;
$abspath = ‘../wordpress/’;