Hi there!
I don't understand why you write the formula in both A1 and A2 and use both of them to copy.

I wrote the formula:
=[File2_details.xls]Sheet1!A1*[File2_details.xls]Sheet2!A1/[File2_details.xls]Sheet3!A1

and when I copy this down to A2, A3, A4 etc I get the following result:
Cell A2: =[File2_details.xls]Sheet1!A2*[File2_details.xls]Sheet2!A2/[File2_details.xls]Sheet3!A2

Cell A3: =[File2_details.xls]Sheet1!A3*[File2_details.xls]Sheet2!A3/[File2_details.xls]Sheet3!A3

Cell A4: =[File2_details.xls]Sheet1!A4*[File2_details.xls]Sheet2!A4/[File2_details.xls]Sheet3!A4

which all seems to be correct if I didn't misunderstand anything.
Of course you must make sure that the references are relativ in cell A1, meaning they should be A1 and not $A$1.

Kind regards
Bjorn