A spongy feel to the clutch pedal, grinding of gears when shifting, long pedal travel, and hydraulic leaks under the car are all signs that one or more components of the system have failed. If bleeding doesn't work, you're on the right track. We have a great article on the master & slave cylinder replacement that has some great info here:
Porsche Boxster Clutch Hydraulics Overhaul (Master Cylinder & Slave Cylinder Replacement) - 986 / 987 (1997-08) - Pelican Parts Technical Article.