VBA code in Excel effecting other other excel worksheet/ workbook

I have VBA code in Excel which restrict access to a workbook depending on the user login detail, the workbook contains 11 sheets, worksheet are asigned to different user depending on the user login detail The problem I have is when i open other worksheet or workbook the VBA code starts to effect the other worksheet/ workbook, is there a way I can stop this from happening.

please help

please find code attached



Private Sub Workbook_BeforeSave(ByVal SaveAsUI As Boolean, Cancel As Boolean)
For Each sh In ActiveWorkbook.Sheets
If sh.Name = "cover" Then
Sheets("Summary").Visible = True 'Must have at least one sheet open
GoTo nEXTsH
End If
Sheets(sh.Name).Visible = False 'Hide all other sheets on Close

nEXTsH:
Next sh
End Sub

Private Sub Workbook_Open()
USN = Environ("USERNAME")

'Expose all sheets for Administrator only.
If USN = "dave" Then
For Each sh In ActiveWorkbook.Sheets
sh.Visible = True 'Expose sheet for Administrator only
Next sh
Exit Sub

'Unhide Summary + users own sheet only
Else
For Each sh In ActiveWorkbook.Sheets
If sh.Name = "Summary" Then
Sheets("Summary").Visible = True
ElseIf sh.Name = USN Then
Sheets(USN).Visible = True
Else: Sheets(sh.Name).Visible = False 'hides all other sheets
End If
Next sh
End If

End Sub