Avoid multiple application instances

//reference http://odetocode.com/blogs/scott/archive/2004/08/20/the-misunderstood-mutex.aspx

[STAThread]
static void Main()
{
   using(Mutex mutex = new Mutex(false, @"Global\" + appGuid))
   {
      if(!mutex.WaitOne(0, false))
      {
         MessageBox.Show("Instance already running");
         return;
      }

      GC.Collect();
      Application.Run(new Form1());
   }
}