Hot to make alert box appear on the same page not on bank

Question

I want to display the alter message on the current  page when I click on the button not on the blank page 

 

please help

T

string alertMessage = "<script language=\"javascript\" type=\"text/javascript\">";

            alertMessage += "alert('No quiz avalible');";
            alertMessage += "window.location.href=\"";
            alertMessage += "View.aspx?Id=" + Request.QueryString["Id"].ToString();
            alertMessage += "\";";
            alertMessage += "</script>";

            ClientScript.RegisterClientScriptBlock(GetType(), "alertMessage ", alertMessage);

hank you