Submenus are disappearing

I am using Fusion wordpress theme and recently added WP e-commerce to have a shopping cart option. Now, for some reason, on my navigation menu, subpage menus disappear when you attempt to click on them.

http://www.jazzykat.net

For example when you hover over “Costs” you see the 3 subpages come up underneath, but as soon as you move down to try to click on them, they disappear. I have no idea how to fix this and it does it on any browser i try. Please help.