I have two sheets in a work book

SHEET ONE providing source data ex: A1 to A3 is changing and so is SUM A1:A3
(example are three sets of A1:A3 data)
And another factor lets say B1 is also changing.

A A A---------B
1 1 2 3 4
2 1 2 3
3 1 2 3
4 3 6 9

SHEET TWO ( IF F1=B1 then A1='sheet1' A4 .... and so on for B1='sheet' A4,
C1='sheet1'A4 ... REMEMBER that B1 and F1 is constantly changing so that the
data (A4) being plugged appropriately )

A B C................F
1 3 6 9................4

So if I do Isnumber, only the last (C1) shown as TRUE, all other isnumber=0
(even though it still shows the number)

Now I want to sum A1:C1 (sheet 2), it only give me Zero "0" , IS THERE ANY
WAY that I GET AROUND and SUM them ???