Suddenly stopped working in May.

WP ecommerce Version 3.8.14.3

I have a client who just asked me to fix this problem – i updated their site to WP 3.9.2, and that didn’t work, so i tried 4.0 – I’ve turned all other plugins off, the ecommerce (with gold cart) is not working.

products show up, but when I click on ‘checkout’ nothing happens.

https://www.ads-software.com/plugins/wp-e-commerce/