My friend had to replace his subs because one of them blew a voice coil and after replacement it worked for a few days then stopped, he also said it would act weird hit normally and then cut out and then work again.
He has 2 RockFord Fosgate P2D212
A clarion 1550w amp.
His amp light is on like it would work but the subs don't hit, checked the RCA's and they checked out ok.
I'm thinking maybe his amp took a crap on him.
I wish he wouldn't have a dealer mess with it...
EDIT: Also the voice coil blowing was his fault for cranking too hard on it, he has now learned his lesson lol.