"Add to Cart" button not responding

The add to cart button in market press on the product pages does not respond, the little wheel just spins indefinitely.
I searched for similar problems, but do not have any redirects, ssl, or trackers as were the issues that fixed other peoples problems.

Prior to it being broken, i had the site up and running, and then i had to back up and reupload the whole site to the same server.
some of the php files were injected with extra white space but i cleaned them all up without touching the rest of the code. there are no syntax errors being pointed out in dreamweaver or excess white space now in the files, so im not sure what else could be causing it. the rest of the site looks and functions exactly as it did before, same plugins and everything.
the only difference is that i added SKU's to the items, but i dont think that could be the culprit, cause when i took them out the problem still occured.
when i go to the shopping cart it is always empty, where previously i had no problem adding to cart and checking out.

the error occurs on all product pages, here is a link to one: http://thegraphixlab.com/hook2/current/content/store/products/abstract-marlin-in-black-and-gold-on-white-shirt/