First of all, it helps if you hit the style change button so that the style says "fatality."

Second, are you sure you have the right button combinations for everyone? If you don't I can post them all for you.

MKDA's fatalities are definately the easiest in any MK game, you shouldn't have any trouble as long as you know what the button combinations are.

yes i have all the button combos for everyone but... im not sure they are the correct ones though. and how far away are you supposed to stand while performing the fatalities.any help will be greatly appreciated

Fatalities can now be performed at any distance, with or without the Fatality stance on, so that's not your problem. Maybe you're using the wrong specific attack buttons? Make sure that you're hitting whatever you set up to be Attack 1, 2, 3, and 4 when entering the Fatality combos. Is it possible that you don't even have the right codes to do the fatalities? Check gamefaqs.com and look up MK: DA for faqs and codes for Fatalities.