Drupal website was hacked? What is the hack that can cause my Drual website to be blank, without showing any message error.. Not be able even I enter .../users, -> blank. It was absolutely brilliantly showing fine.

If you want to see this Drupal website URL, go ahead:

http://fightforhongkongdemocracy.net

Thanks.
There is a guide on drupal.org with multiple troubleshooting methods to resolve white screens with no ouputs: https://www.drupal.org/node/482956