private void button3_Click(object sender, EventArgs e)
    {
         //OleDbCommand cmd = new OleDbCommand();
        System.Data.OleDb.OleDbDataAdapter da;
        //OleDbCommand cmd = con.CreateCommand();
        //OleDbCommand oleDbCmd = new OleDbCommand();
        oleDbCmd.Connection = con;
        con.Open();
        string sql = "SELECT * From Student2 where Enroll = '" + textBox1.Text + "'";
        da = new System.Data.OleDb.OleDbDataAdapter(sql, con);

        OleDbDataReader myReader = oleDbCmd.ExecuteReader();
        OleDbDataReader myReader;
        myReader = oleDbCmd.ExecuteReader();
        int count = 0;

            while (myReader.Read())
            {
                count = count + 1;
            }
            if (count == 1)
            {

                DataTable t = new DataTable();
                da.Fill(t);
                dataGridView1.DataSource = t;
            }
        //}
            else
            {
                MessageBox.Show("Given ID Does not Exist!");
            }


        con.Close();

    }

private void button3_Click(object sender, EventArgs e)
{
    OleDbConnection con = new OleDbConnection("Your connection string");
    OleDbCommand cmd = new OleDbCommand(con);
    OleDbDataAdapter da;
    con.Open();
    string sql = "SELECT * From Student2 where Enroll = '" + textBox1.Text + "'";
    cmd.CommandText = sql;
    da = new OleDbDataAdapter(cmd);

    DataTable t = new DataTable();
    da.Fill(t);
    if (t.Rows.COunt > 0)
    {
        dataGridView1.DataSource = t;
    }
    else
    {
        MessageBox.Show("Given ID Does not Exist!");
    }
    da.Dispose();
    cmd.Dispose();
    con.Close();
}