If you are wondering why my cat wont use litter area anymore then I think I can help you.
A while back now, my cat stopped using its litter box and it surprised and puzzled me for a while.
I did some research and asked the right people though and here are some of my top tips.
Make sure they have a clean litter box - OK we will start off nice and simple.
I am not saying you do not clean the litter box regularly, I'm sure you take good care of your cat but some cats are really picky with things like this.
Try cleaning it out thoroughly once a day for a week and see if it makes any difference to your cats behaviour.
  Scrubs it with water and maybe even try giving them their food near it a few times so they have a place to go immediately after finishing eating and feel comfortable around it.
Treats! - You have to reward cats for good behaviour.
Cats love being rewarded and will give you love and obedience in return.
Do you know what treats they like? If you do then give them that every time they use the litter tray.
A good idea that I have heard is to get the treat and beckon them over to the litter tray and give it to them there.
They will associate treats with the litter box then and you might even catch them trying to get your attention when they go, its quite funny.
Make it fun - you have to make a cat curious.
If they are not curious they will just turn away.
Give them all of their fun toys of maybe even some new ones around the area that you want them to urinate in (the litter box) and they will be there more playing and having fun and more likely to use it.
Reward the good behaviour and you are well on your way to learning why my cat wont use the litter box anymore.