C# 判断不同的用户登录，出现一个问题只能登录一个页面

我在做一个登录窗口，表中有两个用户，一个是管理员，一个是普通用户，我在表中用int型来表示他们的区别，0是管理员的权限，1是普通用户，问题是表中第一个管理员可以登录，第二个普通用户不能登录，请大神指点指点......
private void button1_Click(object sender, EventArgs e)
        {
            if (textBox1.Text == "" && textBox2.Text == "")
            {
                MessageBox.Show("请输入用户名或密码，不能为空");
            }
            else
            {
                if (textBox1.Text != "" && textBox2.Text != "")
                {
                    string str = ConfigurationManager.ConnectionStrings["kecheng"].ConnectionString;
                    SqlConnection con = new SqlConnection(str);
                    con.Open();
                    string strsql = "SELECT * FROM userssss";
                    SqlCommand com = new SqlCommand(strsql, con);
                    SqlDataReader red = com.ExecuteReader();

                    if (red.Read())
                    {
                        string name = red["username"].ToString();
                        string pad = red["passwd"].ToString();
                        int i = Convert.ToInt32(red["userpowsd"]);
                        if (textBox1.Text == name && textBox2.Text == pad)
                        {

                            if (i == 0)
                            {
                                admin f = new admin();
                                f.Show();

                            }
                            else
                            {

                                kaosheng kao = new kaosheng();
                                kao.Show();
                            }
                        }
                        else
                        {
                            MessageBox.Show("不存在该用户");
                        
                        }


                    }
                    con.Close();


                }
                else
                {
                    MessageBox.Show("不好意思，该用户不存在");


                }

            }