SUM in random files in the folder - VBA

I have files in the folder.

how I consolidate in new sheet all the files, to sum for region, products?

OBS: I not know the amount of files in this one folder, so I know that the
these nominated archives for region,

a994.xls region A,

b423.xls
b323.xls region B
....

How to create a look with filename random ? and I not know the quantity file
for region.

But, all the worksheets have format the same.
Necessary they to charts with it, then I want create the table consolidate

thanks
Marina