If error logging was enabled, you would see a fatal error message appear on the screen, but because logging is disabled you only see a blank white screen.
You can temporarily add the following lines to the top of your index.php file in order to see the fatal errors:
error_reporting(E_ALL);
ini_set('display_errors', TRUE);
ini_set('display_startup_errors', TRUE);
|
OR set display_error=On in PHP.ini
Once you can see the errors, you can troubleshoot these.