Sheet change or sheet calculate?

[Cheetahke]

Hi,

I've made a workbook with 15 sheets in it. The first 12 contains each month
of a year, with formula's in most of the cells.
The 13th sheet contains the entire year, with formula's in some of the
cells, and cells than can be changed by someone.
In one of the cells on worksheet 13, when a value changes, the entire
workbook must be recalculated. This cell is "A1".
When someone puts a value in cell "C6" on worksheet 13, the bgcolor of "C6"
and the bgcolor of "C5" must change. So far so good. That works fine, but
when I set folowing code for sheet 13, I get problems in the vba code for
setting the right colors.
Code :
Private Sub Worksheet_Change(ByVal Target As Range)

If Not Intersect(Target, Range("a1")) Is Nothing Then
Call FeestdagInstellen
End If
'With Target
'If Target.Row > 3 Then
'If Not .HasFormula Then
'If Not .Value = "inac" Then
'Target.Value = StrConv(Target.Value, vbUpperCase)
'End If
'End If
'End If
'End With

End Sub
I can not put the entire code from the Modules in here, because it is very
large.