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

namespace WindowsApplication28
{
    public partial class Form1 : Form
    {
        [StructLayout(LayoutKind.Sequential)]
        public struct LASTINPUTINFO
        {
            [MarshalAs(UnmanagedType.U4)]
            public int cbSize;
            [MarshalAs(UnmanagedType.U4)]
            public uint dwTime;
        }
        [DllImport("user32.dll")]
        public static extern bool GetLastInputInfo(ref   LASTINPUTINFO plii);
        

        public long getIdleTick()
        {
            LASTINPUTINFO vLastInputInfo = new LASTINPUTINFO();
            vLastInputInfo.cbSize = Marshal.SizeOf(vLastInputInfo);
            if (!GetLastInputInfo(ref   vLastInputInfo)) return 0;
            return Environment.TickCount - (long)vLastInputInfo.dwTime;
        }

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            this.timer1.Interval = 2000;
            this.timer1.Enabled = true;

        }
        private void timer1_Tick(object sender, EventArgs e)
        {
            long i = getIdleTick();
            this.Text = string.Format("jinjazz说:您已经{0}ms没有动了",i);
            if (i > 10 * 1000)
            {
                this.WindowState = FormWindowState.Minimized;
            }
            else
            {
                this.WindowState = FormWindowState.Normal;
            }
        }
         
    }
}

------解决方案--------------------
另一思路，重载窗体的WndProc，判断其鼠标、键盘消息（我试过什么消息都不判断的话也行）
C# code
        protected override void WndProc(ref Message m)
        {
            base.WndProc(ref m);
            timeOut = 10;
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            if (--timeOut == 0)
                MessageBox.Show("Time is out!");
        }