How to change the procuts from vertical to horizontal?

http://www.pureperformanceracing.net/home/index.php?main_page=index&cPath=65

This is an example of what i am talking about. The items are being showed vertically and not horizontal. It used to be horizontal, but one day it just changed. The problem is that the only thing i was changing was the tpl_header.php and i don't think any of that should affect the middle part.

You could try:

admin/configuration/product listing/Product Listing - Layout Style (set to columns instead or rows)

I don't see any Product Listing - Layout Style

You'll need to install this first:

http://www.zen-cart.com/index.php?main_page=product_contrib_info&products_id=77

Without the Column Grid mod, the products could never have been displaying horizontally. The page referenced is not a product listing but a category/subcategory listing. If the maximum categories per row had been changed, they would be sitting in the center of the column. The float: left; that should control these has been deleted in the stylesheet - without that, the items each occupy their own row at the partial width calculated for multiple display.

A stock stylesheet has:

#logo, .centerBoxContents, .specialsListBoxContents, .categoryListBoxContents, .centerBoxContentsAlsoPurch, .attribImg {
float: left;
}

A look at your stylesheet shows you have commented the whole rule:

/*#logo, .centerBoxContents, .specialsListBoxContents, .categoryListBoxContents, .centerBoxContentsAlsoPurch, .attribImg {
        float: left;
        }*/

If you wanted the logo to not be floated, you need to separate it from the rest of the rule so different styling can be applied to it without messing up the rest; or just comment it out in this case:

/*#logo,*/ .centerBoxContents, .specialsListBoxContents, .categoryListBoxContents, .centerBoxContentsAlsoPurch, .attribImg {
        float: left;
        }

Thank you so much gjh42, that is exactly what was going on, i had commented out the whole piece of code and that messed up everything. I changed it back to normal and is back to how it was.