Maybe you didn't read the fatality right or the source you got it from was flawed. Both work fine for me. Try these.
Fatality 1: forward, back, down, forward, 2 (close range)
Fatality 2: back, down, forward, down, 1 (sweep range)
Hara-Kiri: down, up, down, up, 2

Its either that or its just the xbox controller makes it 10 times harder

alright there must be some trick to doing this. for doing the first fatality
its f b d f A. but everytime i do this it just turns into the ice blast. this is because ice blast is the last part of that code d f a. even my friend tried to do it and it ddnt work. Please Help. Once i get this i can die happy

2 is Y on xbox, not A. Pretty common mistake though, I've fucked that up a few times.

strange....subzeros is the easiest fatality for me

1 = X
2 = Y
3 = A
4 = B
A is the wrong command. Its F, B, D, F + Y

bah.....his second fatality looks better

True. His second is one of the best in the game

agreed ^^^^
i had the same problem with the Y and A butto thing. On gamefaqs it listed A as 2 in the FAQ grrrrrr!