1997 Honda Accord clutch

My son parked the car and said the clutch was fine, when he went to use it the next day the clutch pedal went to the floor, (it had no ressistance) I (dad) put the car in the garage and after looking on the internet and asking quite of few mechanics replaced the master cylinder on the firewall, this did not fix it. I replaced the slave cylinder and tried to bleed the system and it still did not work, if im not mistaken after pumping the clutch for sometime, the clutch should have some resistance and get better through bleeding the system, the system will not bleed after a lot of pumping of the clutch. I went to the master cylinder and took the screw out of the side of the cylinder and very little fluid "if any" is not in the system. Do I have to prime the system some how? Or do I have a air lock in the hydraulic lines?