请教一下，为什么findwindw函数为什么找不到信使服务窗口？

Public Class Form1
    Private Declare Function sndPlaySound Lib "winmm.dll" Alias "sndPlaySoundA" (ByVal lpszSoundName As String, ByVal uFlags As Long) As Integer

    Private Const SND_ASYNC = &H1&
    Private Const SND_LOOP = &H8&
    Private Const SND_MEMORY = &H4&
    Private Const SND_NODEFAULT = &H2&
    Private Const SND_NOSTOP = &H10&
    Private Const SND_SYNC = &H0&
    Declare Sub Sleep Lib "kernel32 " (ByVal milliseconds As Long)
    Private Declare Auto Function FindWindow Lib "user32" (ByVal lpClassName As String, ByVal lpWindowName As String) As Integer

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load


    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim rc As String
        Dim hWnd As Integer
        While hWnd = 0
            System.Threading.Thread.Sleep(3000)
            hWnd = FindWindow(vbNullString, "信使服务")
            If hWnd Then
                rc = sndPlaySound("tada.wav", SND_ASYNC Or SND_LOOP)
            End If
        End While
    End Sub
End Class

换成“我的电脑”就能找到 --------------------编程问答-------------------- 没有句柄 --------------------编程问答-------------------- 无图无易做图

也许就不是信使服务!

补充：VB ,  API