Webshop doesn't send the order forward? Why?!

I can add products to the shopping cart, and can fill in the order form, but when I try to accept the order and send it, the system doesn't move on, it just shows the same page again.

In the very beginning - when I made the first efforts with the order form - I somehow got TWO test orders through. But then as I made some further developments to the layout, the form stopped working. After that I've tried to build the ordering pages again and again - and as simple as possible - but they just won't get alive.

I don't know where to look for the problem, could someone at least try to help me?

This shop will be found in http://www.tuntsa.fi , and from there to the "Tuntsa kauppa", and again to one of those product groups...