I set up a database composed of 16 Tables and I populated these tables from text files.

These text files get updated on a biweekly basis, so I need my tables to be updated on a biweekly basis also. When linking my tables to the text files, I lost all my keys in the linked tables and my relationships were also lost.

I tried to reinstate my relationships but there are all under an "Undeterminate" Relationship type. Is there a way to keep my relationships and my keys in these linked tables?
And is there a way to split linked tables?