The ABS might not have anything to do with the brake issue unless it so happened to come on at the same time. Then it could possibly be an issue with your abs pump or just as simple as a sensor that lost its magnatism. I have a good feeling it is the booster cause if you hear a hissing noise of any sort that is vacuum leaking from the booster. In turn there is no pressure on the diaphram and it is stiff to push. Also check your vacuum line going to the booster to make sure it is not disconnected or dryrotted.