Trying to watch for USB events via WMI but can't seem to display output in winforms

[Luke Herbert]

I am very new to C# and have been trying to get to grips with it by
writing a small tool to detect a USB key being inserted and then backup
user specified files to the key.

I have written some code and been able to construct a WMI query and can
even get the output of this query to display to the console but not to
a TextBox on my form. I fear it is embarassingly obvious but having
looked at a whole heap of books (not read them in their entirety which
would be wiser) I am still no wiser as to why I see nothing. I mean the
'Start capture' message is displayed.

Anyway here is my code (I tired to strip out as much as possible to
isolate the problem). I would be greatfully for any advice.

using System;
using System.Drawing;
using System.Manageme nt;
using System.Windows. Forms;

public class USBWatch : Form
{
public static TextBox txtbox;
static ManagementEvent Watcher watcher = new
ManagementEvent Watcher();

public static void Main()
{
Application.Run (new USBWatch());
}

public USBWatch()
{
//Setup Main form
Text = "USB Watch ";
Size = new Size(500, 600);

//Setup main output textbox
txtbox = new TextBox();
txtbox.Parent = this;
txtbox.BorderSt yle=BorderStyle .None;
txtbox.Multilin e=true;
txtbox.Location = new Point(5, 30);
txtbox.Size = new Size(ClientSize .Width-10, ClientSize.Heig ht -
50);
txtbox.Anchor =
((System.Window s.Forms.AnchorS tyles)((((Syste m.Windows.Forms .AnchorStyles.T op
| System.Windows. Forms.AnchorSty les.Bottom) |
System.Windows. Forms.AnchorSty les.Left) |
System.Windows. Forms.AnchorSty les.Right)));
txtbox.ScrollBa rs = ScrollBars.Vert ical;
txtbox.ReadOnly = true;
txtbox.BorderSt yle = BorderStyle.Fix ed3D;

//Setup START Button
Button startbtn = new Button();
startbtn.Parent = this;
startbtn.Text= "Capture";
startbtn.Locati on = new Point(300, 5);
startbtn.Click += new EventHandler(St artCapture);

//Setup STOP Button
Button stopbtn = new Button();
stopbtn.Parent = this;
stopbtn.Text= "Stop";
stopbtn.Locatio n = new Point(400, 5);
stopbtn.Click += new EventHandler(St opCapture);
}

void StartCapture(ob ject obj, EventArgs ea)
{
txtbox.AppendTe xt("Capture Started \r\n");

//Set watcher scope
watcher.Scope = new ManagementScope ("root\\CIMV2") ;

//Bind to local machine
ConnectionOptio ns opt = new ConnectionOptio ns();
opt.EnablePrivi leges = true; //sets required privilege

//Create event query to be notified on creation of USB device
within 1 second
WqlEventQuery query = new WqlEventQuery() ;
query.EventClas sName = "__InstanceCrea tionEvent";
query.WithinInt erval = new TimeSpan(0, 0, 1); //Notifcation
within 1 second
query.Condition = @"TargetInstanc e ISA
'Win32_USBContr ollerDevice' ";
watcher.Query = query;

//Attach event hander and start watcher
watcher.EventAr rived += new
EventArrivedEve ntHandler(Displ ayEvent);
watcher.Start() ;
}

void DisplayEvent(ob ject obj, EventArrivedEve ntArgs eaa)
{
MessageBox.Show ("USB Event!");
txtbox.AppendTe xt("USB Event!");
}

void StopCapture(obj ect obj, EventArgs ea)
{
watcher.Stop();
watcher.Dispose ();
txtbox.AppendTe xt("Capture Stopped \r\n");
}
}