Drupal Blank pages or "white screen of death" (WSOD)

Problem
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1) If error reporting is turned off, you could be getting a fatal error. On a production site, it is common to have error reporting turned off.

Solution
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2) Either turn on PHP error reporting so it displays a message on the page itself, or check your log files (from the server) to look for the error.

Handle
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3) To enable error reporting, temporarily edit your index.php file 
<?php
error_reporting(E_ALL);
ini_set('display_errors', TRUE);
ini_set('display_startup_errors', TRUE);