Can't click on products in categories in our store

After the update to 1.6

You just enter the shop, then some product category and then products appear. But you are not able to click on any product = noone can buy anything from our shop.

What to do?

Go in the hikashop options of your products listing menus/modules via the menu Display->Content menus/modules and turn on the option "link to the product page".

Thank you very much. Is it possible that it was changing itself while upgrading to 1.6 version?

It's possible.
We changed almost all the Display options in order to support heritage for 1.6.0. So it's possible that the option got reverted to its default value during the update.