archive-custom_type.php doesn't work

Thank you for your fast answer. I didn’t insert any link because I’m working on a local site. As you suggested I think that the problem is that I’m visiting the wrong url. In fact I want to filter my product custom post by category, but clicking on a category link the url is http://mysite/category/mycategory that’s the standard post category url. I don’t have any category.php file and wordpress use the archive.php as fallback. My question is: how can I use standard categories to filter custom posts? I tried also using WP_Query in a category.php page, in this way:

$args = array(
		'post_type' => 'product'
	);

	$the_query = new WP_Query( $args );

and
<?php if ( have_posts() ) : while ( $the_query->have_posts() ) : $the_query->the_post(); ?>
but the returned loop is always empty.

I have a simple sidebar with the list of products categories, when I click on the category link I want to view only the products of this category, in the same way that it works for default posts. If I use $the_query->the_post() in the if statement it fetch all product posts without filter the current category