the order confirmation email is not sent – Magento

how to enable the “order confirmation email” and able to be sent to the customer email?
The email was sent before, but somehow the order is not sent by email anymore. The “Order” and “Order Comments” setting in the System->Configuration->Sale Emails are Enabled.
Where can this go wroing?

Just make a small change in order.php
(public_html/app/code/core/Mage/Sales/Model/Order.php)
First, create one directory structure on the path below, then copy and paste the file to the path below.
(public_html/app/code/local/Mage/Sales/Model/Order.php)
Now, change from
$mailer->setQueue($emailQueue)->send();
to
$mailer->send();

https://community.magento.com/t5/Programming-Questions/the-order-confirmation-email-is-not-sent/td-p/374

or See Video

https://www.youtube.com/watch?v=NycpWVESqhA

Magento, PHP