hhrumph

I have a intermittently amber ABS and red BRAKE light coming on during engine start. Most times it will clear itself and then go out. A couple of times with the lights on, I pushed the brake pedal down hard and it felt as if the pedal went down to the floor. So far I have been able to shut down engine and then restart, the lights went out and Brake pedal felt normal.
Any suggestions, ideas ?
Thanks in advance.