might i suggest editing the wp-config.php and adding
define('WP_DEBUG', true);
or find the line that says
define('WP_DEBUG', false); and change to true
then load the cart and see what errors pop up.
also there is this
http://wordpress.org/extend/plugins/woocommerce-debug-bar/
which works along with http://wordpress.org/extend/plugins/debug-bar/
I have not tested this plugin myself though.
the issue I had with no items appearing in my cart was a plugin called Share your cart
the items were still in the cart, but it would not display them till i clicked checkout.