Hello Stefano,

I am really sorry for the delay of this reply as it is a weekend for us here.
It seems like you have requested before you need to hide this ask button in your site before April 15 2014.
Can you please have a check on this custom css file -> JoomlaFolder/templates/yoo_nano2/css/custom.css
If you would like to show out the Ask button, you can remove it the custom code.

/*===================Stackideas.com Hack==============*/

div#discuss-wrapper .discuss-searchbar { /*15April2014*/

  height:inherit !important;

}

div#discuss-wrapper * {

  box-sizing: initial;

}

div#discuss-wrapper .discuss-item .discuss-item-left {

  width: 77px !important;

}

div#discuss-wrapper .discuss-searchbar .btn-ask {

    display: none;

}

Hope this help.