Apart from other settings overriding your ini, as @ronalds; says, you also have to check your error_reporting level is set to show a low enough level of errors for them to be worthy of being shown at all.
Start on a single page like this:
$arr = array();
// should get you an "undefined offset" error
Then uncomment the first 2 lines, check if there is an .htaccess file in this folder, or above it.
Then check your httpd.conf file carefully, especially for the VirtualHost directives for this site.