<script type = "text/javascript" >
   function preventBack(){window.history.forward();}
    setTimeout("preventBack()", 0);
    window.onunload=function(){null};
</script>

Response.Cache.SetCacheability(HttpCacheability.NoCache);
 Response.Cache.SetExpires(DateTime.Now);

protected override void OnPreInit(EventArgs e)
{
    base.OnPreInit(e);
 
    Response.Buffer = true;
    Response.ExpiresAbsolute = DateTime.Now.AddDays(-1d);
    Response.Expires = -1500;
    Response.CacheControl = "no-cache";
    Response.Cache.SetCacheability(HttpCacheability.NoCache);
}