Option Explicit

Private Sub Workbook_BeforeClose(Cancel As Boolean)
    Application.ScreenUpdating = False
    Dim wsSh As Worksheet
    Sheets(sWarning).Visible = -1
    For Each wsSh In ThisWorkbook.Sheets
        If wsSh.Name <> sWarning Then wsSh.Visible = 2
    Next wsSh
    Application.ScreenUpdating = 1
End Sub
Private Sub Workbook_Open()
    Application.ScreenUpdating = False
    ThisWorkbook.Sheets(sMainSheet).Visible = -1
    ThisWorkbook.Sheets(sWarning).Visible = 2
    Application.ScreenUpdating = 1
    frmIndicateUser.Show
End Sub