can't display the shopping cart or checkout pages

Hi, I'm trying to setup marketpress on a website. Everything works as expected with the exception of the shopping cart and checkout pages. When I click on the shopping cart page, it doesn't go to the shopping cart. I can add products to the shopping cart, but can't view the cart contents, and I can't get to a checkout page. I tried entering the appropriate url for the shopping cart (/store/shopping-cart), but it displays a different existing page for the website. Can anyone tell me what I'm doing wrong? Any help is much appreciated. Thanks in advance.