...
if(验证失败)
{
        //登录失败，提示并跳转到登录页面
       ClientScript.RegisterClientScriptBlock(GetType(), "", "<script>alert(/'登录失败!/');setTimeout(function(){location.href='Login.aspx'},1000);  </script>");
}
else
{
        //登录成功，提示并跳转到主页面
       ClientScript.RegisterClientScriptBlock(GetType(), "", "<script>alert(/'登录成功!/');setTimeout(function(){location.href='Main.aspx'},1000);  </script>");
}
...