void Application_Start(object sender, EventArgs e)
    {
        //在应用程序启动时运行的代码
        checkTimer = new System.Timers.Timer();
        inProgss = false;
        checkTimer.Interval = 5000;
        checkTimer.Elapsed += new System.Timers.ElapsedEventHandler(checkTimer_Elapsed);

    }
    private System.Timers.Timer checkTimer;
    private bool inProgss = false;

    void checkTimer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
    {
        if (!inProgss)
        {
            inProgss = true;
           //执行需要的代码
            inProgss = false;
        }
    }