Drupal reset cron

// Delete cron with PHP

 $num_deleted = 0;

$num_deleted = db_delete('variable')
          ->condition('name', 'cron_semaphore')
          ->execute();

$num_deleted += db_delete('variable')
          ->condition('name', 'cron_last')
          ->execute();

if ($num_deleted > 0)
        echo "Cron cleared. Clear cache!";

--

// Delete flood with PHP

 $num_deleted = 0;

        $num_deleted = db_delete('flood')
          ->execute();

    if ($num_deleted > 0)
        echo "Flood cleared.";


--

// Delete cron with SQL

DELETE FROM `variable` WHERE name = 'cron_semaphore';
DELETE FROM `variable` WHERE name = 'cron_last';

// And CLEAR CACHE before running cron again.