GetBootTime.cs

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

namespace Get_Boot_Time
{
    public partial class Frm_Main : Form
    {
        public Frm_Main()
        {
            InitializeComponent();
        }

        [DllImport("kernel32")]
        extern static UInt64 GetTickCount64();

        public static TimeSpan GetUpTime()
        {
            return TimeSpan.FromMilliseconds(GetTickCount64());
        }

        private void Frm_Main_Load(object sender, EventArgs e)
        {
            lbl1.Text = "Boot Time : " + GetUpTime();
        }
    }
}