connection c# and SQL server 2008 R2

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C#

SQL-Server

SQL-Server-2008

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Hey Every Body,
please Ihave a small problem, hier is my code. This code walk but i cannot give more than one data(or Informations). after that i need to close my WinForm and run it again. where is the Problem? can somed´body help me please.

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.SqlClient;
using System.Data.Common;


namespace Netz_Vorgang
{
    public partial class Form1 : Form
    {
        SqlConnection connection = new SqlConnection("Data Source=STEPHANE-YOTAT\\STEPHANE;Initial Catalog=DBtest;Trusted_Connection=Yes");
        public Form1()
        {
            InitializeComponent();
            try
            {
                connection.Open();
            }
            catch (Exception ex)
            {
                MessageBox.Show("error occured 2 " + ex.Message);
                this.Dispose();
            }
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            
        }

        private void _insert_Click(object sender, EventArgs e)
        {
   

            string com = string.Format("insert into Step values('{0}', '{1}')", (string)(_StepName.Text.ToString()), Int32.Parse(_Dauer.Text));

            SqlCommand com2 = new SqlCommand(com,connection);
            try
            {
                com2.ExecuteNonQuery();
                connection.Dispose();
                MessageBox.Show("successfull");
                _StepName.Text.Equals( "");
                _Dauer.Text = "";
                _StepName.Focus();
                
                this.Update();
            }
            catch (Exception ex)
            {
                MessageBox.Show("error occured 1" + ex.Message);
                this.Dispose();
            }
        }

        private void _show_Click(object sender, EventArgs e)
        {
            SqlCommand connec = new SqlCommand("select * from Table",connection);
            DataSet vds = new DataSet();
            SqlDataAdapter vda = new SqlDataAdapter(connec);
            vda.Fill(vds,"ret");
            dataGridView1.DataSource = vds.Tables["ret"];
            connection.Dispose();
            
        }
    }
}

Please if somebody have another Solution it wellcome. Thanks for ur Help.