Private Sub Workbook_Open()
Dim ws As Worksheet
Application.AskToUpdateLinks = True
On Error Resume Next
For Each ws In ThisWorkbook.Worksheets
If ws.Name <> "Activité" Then
If IsEmpty(ws.[B3]) Then
ws.[B3] = CDate(InputBox("Veuillez rentrer la date du 1er jour de la semaine", "Ouverture " & ws.Name, Date))
If Len(ws.[B3]) = 0 Then MsgBox "Date absente en " & ws.Name, vbCritical
End If
End If
Next ws
End Sub