if (treeView1.SelectedNode.FirstNode != null)<br />
                return true;<br />

public partial class Form1 : Form
    {
        ServiceController[] scServicesA;  //Initial services.
        public ServiceController scTempB;
        public ServiceController scTempA;
        public Form1()
        {            
            InitializeComponent();
            scServicesA = ServiceController.GetServices(); //Initial services.
            int cuentaA = 0; //to count the number of services in CheckListBoxA.
            clbA.Items.Clear();  
            clbB.Items.Clear(); 
            foreach (ServiceController scTempA in scServicesA)
            {
                cuentaA += 1; //Add 1 to the count of services in CheckListBoxA.
                clbA.Items.Add(scTempA.DisplayName + " (" + scTempA.ServiceName + ")" + "\r\n");  //print the services in a CheckListBox "clbA".
           }
            Timer tmr = new Timer(); //timer to periodically get services (scServicesB).
            tmr.Interval = 3000;
            tmr.Enabled = true;
            tmr.Tick += new EventHandler(tmr_tick);
            lblCuentaA.Text = cuentaA.ToString();  //Nª services in CheckListBoxA
        }
         public int cuentaB;  // To count services en CheckListBoxb
        public void tmr_tick(object sender, EventArgs e)
        {
            clbB.Items.Clear();  
            cuentaB = 0;
            ServiceController[] scServicesB;  //services get every 3 sec.
            scServicesB = ServiceController.GetServices();
            

            foreach (ServiceController scTempB in scServicesB)
            {
                clbB.Items.Add(scTempB.DisplayName + " (" + scTempB.ServiceName + ")" + "\r\n");
                cuentaB += 1;             }
            lblCuentaB.Text = cuentaB.ToString();

            if (scServicesA.Equals(scServicesB)) MessageBox.Show("Son IGUALES");  //comparison between the initial services (scServicesA) and the services get periodically (scServicesB).
            else MessageBox.Show("Son DISTINTOS");
        }
    }

if(scServiceA[0] == scScerviceB[0] && scService[1] == scServiceB[1])
{
   // they're equal
}