Why is my female cat that is spayed all of a sudden peeing all over the house after being litter trained 4yrs?

Iv had this cat now for 3yrs and she is spayed and has never peed outside of the litter box, she is now peeing on the carpet nextd to the wall. i have tried everything moving furniture around and cleaning the areas she has peed but she is continuing to urinate in different places WHY>???