C# penjualan dengan data base

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.OleDb;

namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}

private void Form1_Load(object sender, EventArgs e)
{
// TODO: This line of code loads data into the 'dbpenjualanDataSet.penjulan' table. You can move, or remove it, as needed.
this.penjulanTableAdapter.Fill(this.dbpenjualanDataSet.penjulan);
txt1.Enabled = false;
txt2.Enabled = false;
txt3.Enabled = false;
txt4.Enabled = false;
textBox4.Enabled = false;
textBox5.Enabled = false;
textBox6.Enabled = false;
textBox7.Enabled = false;

btnhps.Enabled = false;
btninput.Enabled = true;
btnklr.Enabled = true;
}

private void btninput_Click(object sender, EventArgs e)
{

grp1.Enabled = true;
grp2.Enabled = true;
btnhps.Enabled = true;
txt1.Enabled = true;
txt2.Enabled = true;
txt3.Enabled = true;
txt4.Enabled = true;
textBox4.Enabled = true;
textBox5.Enabled = true;
textBox6.Enabled = true;
textBox7.Enabled = true;


string koneksi = "Provider = Microsoft.Jet.OleDb.4.0;Data Source=D:/Database/dbpenjualan.mdb";
if (txt1.Text != "" && txt2.Text != "" && txt3.Text != "" && txt4.Text != "")
{
try
{
string sql = String.Format("INSERT INTO penjulan(Kode_Barang,Nama_Barang,Harga_Barang,jumlah_Barang)VALUES('{0}','{1}','{2}','{3}')", txt1.Text, txt2.Text, txt3.Text,txt4.Text);
OleDbConnection conn = new OleDbConnection(koneksi);
conn.Open();
OleDbCommand cmd = new OleDbCommand(sql, conn);
cmd.ExecuteNonQuery();
conn.Close();
MessageBox.Show("Simpan Data berhasil!");
txt1.Clear();
txt2.Clear();
txt3.Clear();
txt4.Clear();


}
catch (OleDbException ex)
{
MessageBox.Show(ex.ToString());
}
txt1.Text = "";
txt2.Text = "";
txt3.Text = "";
txt4.Text = "";

}
else
{
MessageBox.Show("Silakan Masukan Data");
}
}




}
}