for releases below PrestaShop 1.5.3
config/config.inc.php
find this line
@ini_set(‘display_errors’, ‘off’);
change to look like this:
@ini_set(‘display_errors’, ‘on’);
PrestaShop 1.5.3+
config/defines.inc.php
find this line
define(‘_PS_MODE_DEV_’, false);
change to look like this:
define(‘_PS_MODE_DEV_’, true);