Updated Summing Data in Another Excel File

Hello,

I'm trying to make one file dependent on another. Here's what I am doing.
I sum data from File B so that the sum will appear in File A even though I manipulate the rows in File B.
So say in File B you have A1 = 1, A2 = 2, A3 = 3 and then in File A you have C1 with the sum of the three of 6. So C1 = 6.
This I have accomplished so far just by having both the windows open and then in the sum formula I'll just select the data from File B.
When I do that I do get rid of the $ signs and use an OFFSET in the sum formula so that when I add or delete a row it includes the old and new data. So right now I have gotten to the point where when I change data in File B the sum in File A is updated just fine.
However if I close File A in Excel, change File B then reopen File A it does not get updated like it does when I have both files open.
Worst case scenario I'll have to keep both files open each time, but since I will not be the only one working on the files, I would like File A to update even though it's not open when File B is changed.

Hopefully that was clear. Any ideas would be greatly appreciated.

MMM

Bump, still looking for any help thanks.