There are a few possible reasons why the cart appears empty when items have been added:
Your cart will appear empty if you have
domain masking set up with your site. Domain masking shows your domain
address instead of the actual page addresses for all pages in your
site, and hides the information about your purchases from the cart.
To fix this, simply remove domain masking and instead change your DNS settings to point to your site.
good reason to remove domain masking is that search engines may not
accept your site and won't list you. Domain masking also prevents you
from sending links to pages other than your homepage.
"Directory Listing Denied" - Internet Security Software
Internet security software set to "anonymous browsing" will cause your cart to return a "Directory Listing Denied" error message. This software removes the information about your purchases from your browser before it reaches our cart, which is why this error is displayed.
Disabling this software corrects the problem. Our cart's checkout pages are secured.
Cookies allow a visitor's computer to memorize the items in their cart while they navigate your site. If this is not working, try deleting your cookies using the instructions in the following document:
Cookies need to be enabled to work with our cart. You can usually check this under "Internet Security" or "Internet Options" settings in your browser. If you've recently installed a Firewall or other security and privacy software, you may also need to make sure it is allowing cookies to be sent to your browser.