Thumbnail Images

I want to have a large picture on my Product page and use a smaller one on my product listing page.
When I turn off thumbnails in the back-end Files -> Images I get the large picture I want on the product page,
but it totally messes up my Product listing page. The product image doesn't show up nor does the product name!

To have a large picture on you product page, you just have to change the value for the options "Product page image width" and "Product page image height" in Configuration > Files.
And enable again the thumbnails.