Unload issue

[snb]

Private Sub Workbook_Open()
    Do
      c00 = InputBox("gebruikersnaam", "inloggen")
    Loop Until Not sheet20.Columns(1).Find(c00) Is Nothing
    
    If c00 <> "" Then
        Do
          c01 = InputBox("wachtwoord", "inloggen")
        Loop Until c01 = Sheet20.Columns(1).Find(c00).Offset(, 1) Or c01 = ""
    End If

    If c00 = "" Or c01 = "" Then
        MsgBox "u bent niet geautoriseerd"
'        ThisWorkbook.Close 0
    End If

    For Each sh In Sheets
      sh.Visible = -1
    Next
End Sub