Why is not this button working?

        private void signinbtn_Click(object sender, EventArgs e)
        {
            if (String.IsNullOrEmpty(nameTxt.Text))
            {
                authTxt.Text = "Failed to authenticate." +
                    "Username can not be empty.";

            }
            else
            {
                if (String.IsNullOrEmpty(PassTxt.Text))
                {
                    authTxt.Text = "Failed to authenticate." +
                        "Password can not be empty.";

                }
                else
                {

                    authTxt.Text = "Success!";
                    //add code here!



                }
            }