Sitting unused for even a few weeks can cause a brake system to develop the problem you're describing. Have some one push the pedal down (slowly) a couple of times and hold it down while you open, then close a bleeder screw on one of the wheel cylinders. You should get a squirt of fluid, and possibly an air bubble. Keep going with all 4 wheels until you get nothing but fluid at all the wheel cylinders. That should get the pedal back. Even a small bubble of air will cause a brake pedal to go all the way to the floor. If the problem comes back during regular use, it will be time to rebuild the master cylinder.
Jerry
