Drupal cron problems - not running , white page
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.
https://www.drupal.org/node/553430 [Solving Drupal Cron problem] page has more details if above steps does not fix your issues.
Following alternate modules can also help in resolving cron related issues.