var prm = Sys.WebForms.PageRequestManager.getInstance();
prm.add_beginRequest(InitializeEventHandler);
prm.add_pageLoaded(PageLoadedEventHandler);

var countOfTries = 0;

function InitializeEventHandler() {
	var aloading = $get('divLoading');
	var acontent = $get('mainContent');
	aloading.style.display = '';
	acontent.style.visibility = 'hidden';
}

function PageLoadedEventHandler() {
    countOfTries = 0;
	AreAllImagesLoaded();
}

function AreAllImagesLoaded() {
	var imagesloaded = 1;
	var images = document.images;
	for (var i = 0; i < images.length; i++) if (images[i].complete == false) imagesloaded = 0;
	countOfTries++;
	
	if (imagesloaded != 1 && countOfTries < 20 && navigator.appName != 'Opera') window.setTimeout("AreAllImagesLoaded();", 500);
	else {
		var aloading = $get('divLoading');
		var acontent = $get('mainContent');
		aloading.style.display = 'none';
		acontent.style.visibility = 'visible';
	}
}