How do i fix the cheats on need for speed pro street for the PS3?

my cheats like "unlockallthings" wont work anymore. how can i fix that? because i have a supra on there with level 4 everything and it does like mid to high 6's on the drag but now i want to be able to buy the level 4 stuff again without having to go thru all the hastle of winning it can anyone help?