Suddenly product detail doesn't show

The site http://soundbitesderby.org.uk/cart/ seems to have suddenly changed. The final product detail screen comes up blank. I cannot pin down when this started but everything else is fine. I am running 1.3.8a still and could do with some pointers as to what tools I can use to debug this please?

Suddenly? You haven't been working on anything?

Since the page works this will generally be an error in a module or template file, not withstanding that if suddenly is correct you might have been hacked.

~Melanie

I hear what you say about hacking but it doesn't look or feel like it. I don't know when it started or how but I guess a file may have gione missing or something and I was looking for some advice on what tools are available to debug this please if anyone can help?

Here you are =-)
http://www.zen-cart.com/index.php?main_page=product_contrib_info&products_id=860

~Melanie

Thanks but I managed to find the cause by downloading the system and using winmerge to find everything tick-a-ty-boo except 1 program had been deleted. I will challenge the ISP on that one!