Clearing a text box when opening a slide

[easy]

How can I clear a text box when I open a slide?
I have used this code from an example ppt

Sub LapTopPreparation()
Dim newstuff As String

newstuff = InputBox("In the box below, enter a step in ensuring
your laptop & printer are fully prepared")
If newstuff <> "" Then
With
ActivePresentation.SlideShowWindow.View.Slide.Shapes(16).TextFrame.TextRange
.Text = .Text + Chr$(13) + newstuff
End With
End If
End Sub

Which allows me to build a list when the macro is run, but I want the
list to be empty when the slide is opened.
I want it to activate when the slide is viewed and not rest by a button
if that is possible