If you get a blank white page it means you have a PHP error that was caused based on the info you copied in. Most often this is becuase the PHP code copied in accidentally replaces, overwrites, or gets pushed between already existing code on the page.

The easiest way to diagnose exactly where the error is, is to turn on Error Logging for the Catalog and then look at the error log generated in the "cache" directory. Depending on what version of zen you are running, you may already have the file needed to turn that on. If not, you'll want to look at this post which has more information on where to find the file and how to activate it: http://www.zen-cart.com/showthread.p...+error+logging