Public Sub test()
 
Dim ex As New Excel.Application
Dim wb As Excel.Workbook
Dim ws As Excel.Worksheet
Dim lngCounter As Long
 
Set ex = New Excel.Application
Set wb = ex.Workbooks.Open("C:\Dokumente und" & _
  "Einstellungen\nrhm\Desktop\Fahrzeuge_test.xls") 'Kompletter Pfad!!
Set ws = wb.Sheets(1)
 
ex.Visible = False
 
 For lngCounter = 2 To 20 Step 1                        'Schleife Anfang
    DoEvents
    If IsDate(ws.Cells(lngCounter, 7)) Then
 
        If DateDiff("d", ws.Cells(lngCounter, 7).Value, Date) >= -14 And _
          DateDiff("d", ws.Cells(lngCounter, 7).Value, Date) < 0 Then
            MsgBox "Ihr TÜV für das ist fällig", vbInformation, "Achtung" & _
            "Autofahrer"
        End If
 
    End If                                              'Schleife Ende
   Next lngCounter
 
End Sub