Brake Pressure Problem

I have a 1990 Acura Integra with a 1.8 litre engine. My brake pedal pushes all the way down to the floor and the pressure in the brake system is almost non existent. My brake fluid is full. I know it could be the master cylinder but how can I check to see if it is or not? Additionally I have two NON-ABS front transaxles but the car is ABS. The ABS light is on in the car. I've been told this doesn't matter but I don't know which master cylinder I need in case that's the problem. First I need help on how to determine whether my problem is a bubble in the brake line or if it is the master.