public Form1()
        {
            InitializeComponent();
        }

        private const string MutexName = "SINGLE_INSTANCE_APPLICATION";
        private bool _firstApplicationInstance;
        private Mutex _mutexApplication;

        private bool CheckApplicationFirstInstance()
        {
            // Allow for multiple runs but only try and get the mutex once
            if (_mutexApplication == null)
            {
                _mutexApplication = new Mutex(true, MutexName, out _firstApplicationInstance);
            }

            return _firstApplicationInstance;
        }


        private void Form1_Load(object sender, EventArgs e)
        {
            // Check first instance or not
            if (CheckApplicationFirstInstance())
            {
                // Yes, this is the first instance
                // Allow this application
            }
            else
            {
                // Close application
                Close();
            }
        }