Excel 2007 : Averaging no blanks and no zeros over several Sheets

Hello I am looking for some help with averaging cells over 20 plus sheets. I do not want blanks or zeros counted. This is what I have used with a few variants but I do not get anywhere with it.

=SUM('WK1 Mon'!D13:'WK1 Tue'!D13:'WK1 Wed'!D13:'WK1 Thu'!D13:'WK1 Fri'!D13:'WK2 Mon'!D13:'WK2 Tue'!D13:'WK2 Wed'!D13:'WK2 Thu'!D13:'WK2 Fri'!D13:'WK3 Mon'!D13:'WK3 Tue'!D13:'WK3 Wed'!D13:'WK3 Thu'!D13:'WK3 Fri'!D13:'WK4 Mon'!D13:'WK4 Tue'!D13:'WK4 Wed'!D13:'WK4 Thu'!D13:'WK4 Fri'!D13:'WK5 Mon '!D13:'WK5 Tue'!D13:'WK5 Wed'!D13:'WK5 Thu'!D13:' WK5 Fri'!D13)/sumproduct/(countif(indirect(""&'WK1 Mon'!D13:'WK1 Tue'!D13:'WK1 Wed'!D13:'WK1 Thu'!D13:'WK1 Fri'!D13:'WK2 Mon'!D13:'WK2 Tue'!D13:'WK2 Wed'!D13:'WK2 Thu'!D13:'WK2 Fri'!D13:'WK3 Mon'!D13:'WK3 Tue'!D13:'WK3 Wed'!D13:'WK3 Thu'!D13:'WK3 Fri'!D13:'WK4 Mon'!D13:'WK4 Tue'!D13:'WK4 Wed'!D13:'WK4 Thu'!D13:'WK4 Fri'!D13:'WK5 Mon '!D13:'WK5 Tue'!D13:'WK5 Wed'!D13:'WK5 Thu'!D13:' WK5 Fri'!F:N,"<>0")

I have also used =sum(sheet cell)/countif(sheet cells, "<>"0)

any ideas please