public static class ServiceGlobals // Globals
{

    public static System.Timers.Timer _timer = new System.Timers.Timer();
}

protected override void OnStart(string[] args)
        {

                    ServiceGlobals._timer.AutoReset = false;
                    ServiceGlobals._timer.Interval = (3000);
                    ServiceGlobals._timer.Elapsed += new System.Timers.ElapsedEventHandler(_timer_Elapsed);
                    ServiceGlobals._timer.Enabled = true;
                    ServiceGlobals._timer.Start(); // Start timer
        }

if (ServiceGlobals._timer.Enabled) // Check if the timer is running
{
    // Return error.........

}