One place to start is to put this at the top of your index.php file in the web root:
<?php
error_reporting(E_ALL);
ini_set('display_errors', TRUE);
ini_set('display_startup_errors', TRUE);
?>That'll show you any fatal errors in PHP. When Drupal encounters one of those it shows a blank page, unless you put that code in (or set it up in php.ini)... paste back here what the error message is that you receive, if any 
Joined: 08/14/2007