Well, it could be any of the above... Master cylinder, a cut bad brake line, or air in the lines... My guess is the master cylinder, because even if 3 of the 4 lines were good, and if theres some air in the lines, there should still be some pressure... But I dont know for sure, thankfully Ive never had this problem... ::knocks on wood::

And I honestly wouldnt be driving the car like that, I wouldnt depend on just the ebrake for daily driving... From the post it sounded like youve been driving it here and there... I would have it towed to a shop in all honesty...