Magento V1.8 one page checkout not loading payment information

As it has been said in the comments the error is located in the checkout.xml.

Here is the faulty code in the custom template:

<block type="checkout/onepage_payment_methods" name="checkout.payment.methods" as="methods" template="checkout/onepage/payment/methods.phtml">

And should be replaced by:

<block type="checkout/onepage_payment_methods" name="checkout.payment.methods" as="methods" template="checkout/onepage/payment/info.phtml">

This error was found on a templatemonster template.

There is a problem with the markup in the payment section.
When the shipping method step is completed this js should be executed:

$('checkout-'+response.update_section.name+'-load').update(response.update_section.html);

response.update_section.name is payment-method

but $('checkout-payment-method-load') returns null because there is no element with that id in your DOM.
Make sure that this file in your theme checkout/onepage/payment/info.phtml has the following content:

<dl class="sp-methods" id="checkout-payment-method-load">
   <!-- Content dynamically loaded. Content from the methods.phtml is loaded during the ajax call -->
</dl>