RequiredFieldValidator and OnClientClick Together

function showContent()

{

    // if you need one group use    

    // Page_ClientValidate('VGFillHours');

    if (Page_ClientValidate())  //validates all groups

    {

        document.getElementById("<%=ImgAjaxloaderClarification.ClientID %>").style.display = "block";

    return true;

    }

return false;

}