1. Have these lines in the PHP script you're calling from the browser (typically index.php):
error_reporting(E_ALL);
ini_set('display_errors', '1');
2.(a) Make sure that this script has no syntax errors
—or—
2.(b) Set display_errors = On in your php.ini
Otherwise, it can't even run those 2 lines!
You can check for syntax errors in your script by running (at the command line):
php -l index.php
If you include the script from another PHP script then it will display syntax errors in the included script. For example:
index.php
error_reporting(E_ALL);
ini_set('display_errors', '1');
// Any syntax errors here will result in a blank screen in the browser
include 'my_script.php';
my_script.php
adjfkj // This syntax error will be displayed in the browser