Continuously updated sums across separate workbooks

Hey,
I am a new member and relatively inexperienced with excel. I read about how to sum across workbooks. =SUM('C:\TABLES[file.xls]sheet 1'!$A$1)
This works just fine....One time. I close the workbook that I am summing to from A1 of sheet 1 of file.xls. A1 of file.xls is itself a sum of a series of cells in sheet 1. =SUM(A3:A50)
Each time I add to the sum in the A column in file.xls A1 will reflect this. However if I add numbers to the A column of file.xls and close and save it, after entering the formula in "current workbook.xls" (the file name I am summing to across workbooks) the cell in current workbook upon being opened again will not reflect this new sum in cell A1 of file.xls

I want the sums to update(I don't want to have to re enter the formula every time I put a new number in the series from file.xls, and I want them to be summed across workbooks. I do not want them in the same workbook on different worksheets.

='C:\TABLES[file.xls]sheet 1'!$a$1
note you will have to select this box, click on the text on the top of excel program then hit enter to "refresh"

it will update (from the file.xls) you just have to request it to do so