If you are having products, but when you click on ADD TO CART, you might face a problem, where it wont get added to your shopping cart and it will keep showing, SHOPPING CART EMPTY, then here are the possible fixes ,
- Reindex data.
- Clear the cache
- Run the database repair tool
- Change the session from FILES to DB from local.xml
- Increase the session time from System Configuration Web Cookie Management
Article source: http://www.learnmagento.org/magento-tutorials/products-not-adding-to-magento-cart/