C# ADO.NET 两个sql对同一个数据库操作 连接开关上有有关问题

求教：C# ADO.NET 两个sql对同一个数据库操作 连接开关上有问题
SqlConnection conn = new SqlConnection(Connection.GetConnection());
 
        public PsdChange()
        {
            InitializeComponent();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            this.Close();
        }
        void Change_key()
        {
            if (txtB2.Text == txtB3.Text)
            {

                conn.Open();
                string sql1 = "update Password set psd='" + txtB2.Text + "'";
                SqlCommand cmd1 = new SqlCommand(sql1, conn);
                int count = cmd1.ExecuteNonQuery();
                if (count == 0)
                { MessageBox.Show("Key错误！"); }
                else 
                {
                    MessageBox.Show("修改成功！", "Key修改提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
 
                }
 
            }

            else
            {
                MessageBox.Show("Two keys are different!");
            }
        }
        private void button1_Click(object sender, EventArgs e)
        {
 
            conn.Open();
            string sql = "select * from Password where psd='"+txtB1.Text+"'";
            SqlCommand cmd = new SqlCommand(sql, conn);
            SqlDataReader reader = cmd.ExecuteReader();
          try
            {
                if (reader.Read() == true)
                {
 
                    Change_key();
 
                }
                else
                {
                    MessageBox.Show("The first key is error!");
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
            finally
            {
                reader.Close();
                conn.Close();
            }
        }