Does my power break booster need to be changed?

Its a mercedez AMG CL 5 something. I know there's a 5. I believe its a 2007 or 2006 it was a friends car but I bought it from him and the breaks are hard to press down when I try to stop and. The ABS light comes on and I'd have to pull over and shut off the car cause it will stall and I'd have to was a few hours before I can start the car