My cat is peeing on the carpet.?

Your cat may have a urinary tract infection. That makes it hurt for them to go pee and they think that the litter box is what is hurting them. Doesn't make much sense, but that happened to my cat when he suddenly stopped using his litter box. If you talk to your vet and think that might be the problem then you should get the cat to the vet quickly because the cat is in pain and I think it can become a serious threat to her health.