Lập trình c# Window form

Đây là source code đăng nhập và hiện thị thông tin của sinh viên bao gồm kết nối cơ sở dữ liệu:

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

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

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void btnlogin_Click(object sender, EventArgs e)
        {
            SqlConnection con2 = new SqlConnection(@"Data Source = WELCOM - PCSQLEXPRESS; Initial Catalog = Test; Integrated Security = True");
            SqlDataAdapter sdt = new SqlDataAdapter("Select Cont (*) from login where id='"+txtid.Text+"'and pass = '"+txtpass.Text+"' ",con2);
            DataTable dt = new DataTable();
            if(dt.Rows[0][0].ToString()=="1")
            {
                this.Hide();
                Form3 ss = new Form3();
                ss.Show();
            }
            else
            {
                MessageBox.Show("Login Failed");
            }
            
            
        }

        private void chcheck_CheckedChanged(object sender, EventArgs e)
        {
            if (chcheck.Checked)
            {
                txtpass.UseSystemPasswordChar = false;
            }
            else
            {
                txtpass.UseSystemPasswordChar = true;
            }
        }
    }
}

Thông tin sinh viên:

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

namespace Login
{
    public partial class Form3 : Form
    {
        SqlConnection conn;
        public Form3()
        {
            InitializeComponent();
        }

        private void Form3_Load(object sender, EventArgs e)
        {
            string constring = @"Data Source=WELCOM-PCSQLEXPRESS;Initial Catalog=Test;Integrated Security=True";
            conn = new SqlConnection(constring);
            conn.Open();
            HienThi();
        }

        private void Form3_FormClosing(object sender, FormClosingEventArgs e)
        {
            conn.Close();
        }
        public void HienThi()
        {
            string sqlselect = "Select From hocsinh";
            SqlCommand cmd = new SqlCommand(sqlselect, conn);
            SqlDataReader dr = cmd.ExecuteReader();
            DataTable dt = new DataTable();
            dt.Load(dr);
            dssv.DataSource = dt;
        }

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

Lỗi của mình gặp phải là Progam doesnot contain a static Main method suitable for enty point? ai giúp mình với