c#新手求助，窗体不能显示

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;

namespace WindowsFormsApp5
{
    public partial class Form1 : Form
    {
        private int nCounter;
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            this.nCounter = 50;
            this.ShowCounter();
        }

        private void btnInc_Click(object sender, EventArgs e)
        {
            this.nCounter++;
            this.ShowCounter();
        }

        private void btnDes_Click(object sender, EventArgs e)
        {
            this.nCounter--;
            this.ShowCounter();
        }

        private void btnMsg_Click(object sender, EventArgs e)
        {
            string strMsg = "当前计数器=" + this.nCounter.ToString("D8");
            MessageBox.Show(strMsg, "提示");
        }
        private void ShowCounter()
        {
            string strMsg = "当前计数器=" + this.nCounter.ToString("D8");
            this.lblResult.Text = strMsg;
        }
    }

照着书敲的代码，为什么不显示窗体

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;
 
namespace WindowsFormsApp5
{
    public partial class Form1 : Form
    {
        private int nCounter;
        public Form1()
        {
            InitializeComponent();
        }
 
        private void Form1_Load(object sender, EventArgs e)
        {
            this.nCounter = 50;
            this.ShowCounter();
        }
 
        private void btnInc_Click(object sender, EventArgs e)
        {
            this.nCounter++;
            this.ShowCounter();
        }
 
        private void btnDes_Click(object sender, EventArgs e)
        {
            this.nCounter--;
            this.ShowCounter();
        }
 
        private void btnMsg_Click(object sender, EventArgs e)
        {
            string strMsg = "当前计数器=" + this.nCounter.ToString("D8");
            MessageBox.Show(strMsg, "提示");
        }
        private void ShowCounter()
        {
            string strMsg = "当前计数器=" + this.nCounter.ToString("D8");
            this.lblResult.Text = strMsg;
        }
    }