Application.Exit() And FormClosing Event In .net?

I have a single windows form application that is running in system tray icon.If the user press X button of the windows form a messagebox is displayed with Yes and No ( Yes ->close the form---No->keep the form running in system tray icon).I was thinking to prevent the scenario when the user open another instance of the application when there is already an instance running so i have used this code :

If Process.GetProcessesByName(Process.GetCurrentProcess.ProcessName).Length> 1 Then
MessageBox.Show("Another instance is running", "Error Window", MessageBoxButtons.OK,
MessageBoxIcon.Exclamation)
Application.Exit()
End If

The problem is that when i want to test this the message is displayed but after i press ok, a new messagebox appears (that one from Private Sub Form_FormClosing ).If i choose NO i will have to instance running!I have read that Application.Exit fires the Form_FormClosing event.Is there any possibility to cancel the triggering of the Form_FormClosing event?'this is the formclosing
procedure

Private Sub Form_FormClosing(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
Try
Dim response As MsgBoxResult
response = MsgBox("Are you sure you want to exit", CType(MsgBoxStyle.Question + MsgBoxStyle.YesNo, MsgBoxStyle), "Confirm")

[code]....