I have 2 maine coons, both spayed and a male cat, breed not known who has been neutered. My Siamese was 14 and died recently. I am wondering why all of a sudden my 7 year old mutt (Alyce) is not using the litter boxes - both are scooped every other day and one is not even being used at all. She is boxed trained and up until about a week after Sassie died she was using the box. HELP!!