Drupal cron job is really easy to setup. However for some old running websites cron job stops working after updating drupal to new version. For one of my websites I had similar issue. The cron job was not running. Neither automatically not manually. Running cron job used to return a blank white page, which means you dont know what the issue is. I even tried installing poormanscron module still it used to fail.
The solution was simple , first disable PHP filter module. Then Run the cron manually, after that enable PHP filter module. Cron will run fine after that.