Custom add to cart for vm product module

[pm4698]

Hello there,

I use VM 2.6.12 with joomla 2.5.x

I want to use custom add to cart button to virtuemart product module.

I found the file in my overrides template folder in html/mod_virtuemart_product/default.php.
Inside there, i can see a line like this: echo  mod_virtuemart_product::addtocart ($product) ;

If i try to change this with this:
<span class="addtocart-button-cat">
                           <input type="submit" name="addtocart"  class="addtocart-button-cat" value="<?php echo $button_lbl ?>" title="<?php echo $button_lbl ?>" />
                        </span>

which is actually the code i want and its shows also to category view, then i get my desired button but when i try to click this, nothing happens at all.

Any ideas?