a blank page means that a php error is occurring but error reporting is turned off.
to turn error reporting on, add the following code at line 1:
<?php
error_reporting(E_ALL);
ini_set('display_errors','on');
?>
once we know what the error is, we will be able to troubleshoot the cause.
The session timeout is set in the php.ini file, see this post at webmaster world for more details:
12812.htm