If the "Add to Shopping Cart" button is not appearing the item might be out of stock. Learn more about item availability.
If the item is available try clearing your cache. Most web browsers temporarily store a local copy of every page you visit. Clearing your cache deletes those files and makes room for new ones. Go to the "Cache" or "Temporary Internet Files" option on your browser (on Firefox, go to "Tools" and choose "Clear Private Data"; if you use Internet Explorer, go to "Tools" and choose "Internet Options"), and delete the files stored in your cache.