First of all- clean up all of the piles of poop! That's disqusting-- It's no wonder your cat isn't going in the litter box-she thinks the whole house is one big litter box!
Next, get a new litter box, and make sure you fill it with fresh litter--use the kind that she was originally using back when she was going in the box. Show her the litter and sit her in it every morning when she wakes up and after every meal. When she does have an "accident" don't scold her, simply move the poop off the floor, drop it in her litter box, and then sit her in the litter and help her bury it--then remove it so the litter box stays CLEAN. Sorry to say, but I think you are the one at fault here for not keeping her litter clean--would you want to poop in a toilet that had heaping piles of turds up to the rim? Well would you?
The Original Male Kitten.