404 page not found when using main menu

My site is phoenicispublishing.com
I’m using Twenty Thirteen theme and WP e commerce

The menu was working until recently – it now displays “404 page not found” when I try to use the menu to take me to the products categories that are in the menu.
I have inserted two images in the home “Shop” page with url links to my product categories – when I click on these images, they do take me to the product category pages.
The menu was still working for a after I set up these image links, so I don’t think this caused it (?).
The address that the images takes me to though is different to the address that the menu takes me to – the menu takes me to pages that are “wpsc_product_category” followed by the product category name (these are the ones that are showing “404 page not found”) while the image links go to addresses that say “products-page-2” followed by the product category name.
So I think this means that I have set something up incorrectly and have my products on a created page rather than where they should be in a product category.
I really don’t know and am at a loss as to what to do now.
I have tried uninstalling WP e commerce and reinstalling it – this did work at first but when I checked back on my website the next day, the menu was again not working.
If somebody knows why this is happening and could explain the solution to me, I would really appreciate the help.