How do you discover which code section a mistake happens in, when the site done on Joomla provides me with a Whitened Screen of Dying?

I know which module fails, and under what condition (it's a slideshow module, also it fails when among the products to show are of video type), but I must check what devote the code it fails in, with the hope of possibly fixing the issue myself (I'm not the initial developer, and i'm not fluent in PHP yet).

You have to enable error confirming inside your atmosphere. It's disabled automatically because of security concerns. I believe the simplest way is always to place the following lines of code at first of the joomla installation's index.php file:

ini_set('display_errors','On'); 
error_reporting(E_ALL);

Once you are done debugging make sure you remove or comment out individuals two lines.