As always (since you are not the first to ask this):
- either your product system consists of only one process or very few processes that do not have any environmental impacts (check the product system statistics to see how many processes you have, check the inventory in the calculation to see if you have elementary flows there);
- or your LCIA method does not fit to your database; you see this for each single process also, in the LCIA impacts sheet, if you have impacts in categories that you expect, or not.
Hth,
Andreas