I need somebody familiar with an older Joomla website to repair a paypal checkout page

I am with a club that hosts a rally yearly with an online registration. when you click the link to register online, it doesn't show the page with the prices and ability to check out, it only says your cart is full. The link is:
http://www.wiscbmwclub.com/#content.
If you go to the Dells Rally tab and click on registration, then click on ' online registration ', it should direct you to a cart page with the option for adult or child registration