Cell function problem

The below formula is to return the quantity of the product from another sheet.
=VLOOKUP(MID(CELL("filename"),FIND("[",CELL("filename"),1)+1,10),'Z:\PartList\[DESC.XLS]Sheet1'!$A:$C,3,0). I have individual sheets for products and one master sheet for quantity.All the file name for the products is the file name itself. So I can use the above formula.
But the problem is when I press F9 for one product, the quantity for that product is applied to all the open files with the above formula. I know the problem is with =Cell("filename").
Hope the problem is explained well. Need attachments? Any solution to stop changing quantity in all open files.
Thanks,
Itty.

Rather than CELL("filename") you need to use a cell reference (any cell reference) otherwise the filename given is for filename of the last cell you changed, so try changing your 2 CELL functions to

CELL("filename",A1)

Cool tip. I was afraid that whether somebody will be able to understand my problem.
Thanks for your guidence.