If you get white screen of death, you might want to make sure your syntax is valid by putting a
die('yes it works');
statement first. If you see that as output, it means you don't have a syntax error.
Once you are sure it's not a syntax error, you should probably put in something like this to make sure the script will barf up any errors you might encounter:
error_reporting(E_ALL);
if (!ini_get('display_errors')) {
ini_set('display_errors', 1);
}
If you are still getting a white screen of death, you might consider looking in the php error log.
My guess is that there's either a syntax error OR you don't have the XML extension enabled.