function check_ads() {
            var ads = document.getElementsByTagName('iframe');
            var visible_ads = 0;
            for(a=0; a<ads.length; a++) { 
                visible_ads++;
                if(ads.item(a).style.display == 'none' || ads.item(a).style.visibility == 'hidden' || ads.item(a).parentNode.style.display == 'none' || ads.item(a).parentNode.style.visibility == 'hidden') {
                    ads.item(a).style.display = 'block';
                    ads.item(a).style.visibility = 'visible'
                    ads.item(a).parentNode.style.display = 'block';
                    ads.item(a).parentNode.style.visibility = 'visible';
                }
            }
            if(visible_ads == 0) {
                return ads_error();
            }
        }