1. Check for leaks on the master and slave cylinder and lines.
2. Bleed the system. Pump it up have some one hold the pedal down and open the bleed screw. It is located on the slave cylinder. Close the bleed screw. Repeat several time you will have to pull the pedal off the floor and pump it up till it feels nice before repeating.
3. Take out the trans and look for clutch failure.