Items not being added to cart in Joomla 2.5.6, VM 2.6.4?

Question

Joomla

There is a site lozhki-luzhniki.ru. When you try to add products, they are not added. According to the site owner, this happened after adding the Top of the page module for scrolling up the page, the "Write us" module - you can see it at the bottom, and the "Callback" module - I wrote it using Fancybox. Whether the shopping cart worked normally before me, I don’t know, I didn’t see it myself, although I’m not a Joomla specialist, I specialize in layout, but I doubt that my actions could somehow affect the operation of the store. Although there were some oddities with styles when setting up modules. Joomla 2.5.6/Virtuemart 2.6.4