C#

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

        }

        private void button1_Click(object sender, EventArgs e)
        {
            Email_Client.Form2 Email = new Email_Client.Form2();
            Email.User.Text = textBox1.Text.ToString();
            Email.Pass.Text = textBox2.Text.ToString();
            Email.Show();
            this.Hide();
        }

        private void textBox1_Leave(object sender, EventArgs e)
        {
            StreamWriter Writer = new StreamWriter(Application.StartupPath + "/acct/info/user.user");
            Writer.WriteLine(textBox1.Text);
            Writer.Close();
        }

        private void textBox2_Leave(object sender, EventArgs e)
        {
            StreamWriter Writer = new StreamWriter(Application.StartupPath + "/acct/info/pass.user");
            Writer.WriteLine(textBox2.Text);
            Writer.Close();
        }

        private void textBox1_Enter(object sender, EventArgs e)
        {
            if (checkBox1.Checked == true)
            {
                StreamReader userreader = new StreamReader(Application.StartupPath + "/acct/info/user.user");
                textBox1.Text = userreader.ReadToEnd();
                userreader.Close();
            }

        }

        private void textBox2_Enter(object sender, EventArgs e)
        {
            if (checkBox2.Checked == true)
            {
                StreamReader passreader = new StreamReader(Application.StartupPath + "/acct/info/pass.user");
                textBox2.Text = passreader.ReadToEnd();
                passreader.Close();

            }
        }

        internal static void DestroyHandle()
        {
            Form1.ActiveForm.Dispose();
        }
    }
}

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

namespace ModeDifféré
{
    public partial class Form6 : Form
    {
        public Form6()
        {
            InitializeComponent();
        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {

        }

        private void Form6_Load(object sender, EventArgs e)
        {
          
            string sConnection = @"Data Source=Admin-PC\MSSQLSERVER,1433;Initial Catalog=GMAO;User ID=sa;Password=sa;";
            string sSQL = "SELECT Nbt FROM 4BT; ";
            SqlConnection conn = new SqlConnection(sConnection);
            SqlCommand comm = new SqlCommand(sSQL, conn);
            SqlDataReader dr = null;
            try
            {
                comm.Connection.Open();
                dr = comm.ExecuteReader();
                while (dr.Read())
                    comboBox1.Items.Add(dr[0]);
            }
            catch (SqlException ex)
            {
                MessageBox.Show(ex.Message);
                return;
            }

            dr.Close();
            comm.Connection.Close();
        }
    }
}

Specifid SQL server name not found:Admin-PC\MSSQLSERVER,1433