计时器结束表格

Question

我在vb.net上做了一个lanhouse，当计时器1打勾（15分钟）时，我想要关闭表单。

Dim acabou As Boolean = False
Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick
    If acabou = False Then
        acabou = True
        MsgBox("O teu tempo na lan house acabou.")
        Browser.Close()
        sistemaoperativo.Close()
        loginoperativo.Close()
        paint2.Close()
        painti.Close()
        musica.Close()
        calculadora.Close()
        haskear.Close()
        haskear1.Close()
        Button1.Enabled = True
        Button2.Enabled = False
        Timer1.Enabled = False
        Timer1.Stop()
        acabou = False
    End If
   End Sub

表格（浏览器，sistemaoperativo等）不要关闭