Error 3 beeps

hello.

I need some help in this big problem, i google it every where.

In macbook pro, i dont have any light in the keyboard and when i try to shut down the pc. the mac goes off but keep producing always 3 beeps in a black screen. The only way to keep it mute is forcing the shutdown on the buton.

I tested the memory and is ok, i dont have ideia what to do, can anyone helpe me please.