If the clutch is on the floor then either the hydraulics are not working or the clutch system has failed in the bell-housing.
Right first thing first, check your hydraulics. Make sure they work. Basic stuff first which I reckon you have done, check the fluid, make sure there is fluid down at the slave too.
I'd then pull the slave out, don't disconnect it from the lines though. Have a look in the bell-housing with a torch and see what you can see. If you stick something in and prod the fork gently (watch the rod doesn't fall off - pest to refit in there) you should be able to tell if the fork is just flapping in the wind. If all APPEARS OK in there have an apprentice push the clutch a bit while you push something into the slave to stop the piston popping out - it should obviously exert a fair bit of force when the pedal is pressed, you should have to fight with it. This will only go so far to check for a leaking seal mind you but it would need to be pretty bad if you cannot build any pressure at all so should be able to test by hand.
I did this on my own once and rigged up a contraption with a piece of rod or something, cable ties and something over the rod that had give but wouldn't let the piston pop out.
If the hydraulics check out then it could be that the clutch cover has failed, there is a wire band that goes round under the diaphragm spring, if this breaks the clutch cover spring fingers won't pivot and therefore move much, giving you exactly what your describing with bite point on the floor and unable to change gears.
With any luck this will be hydraulics- fluid leak/seal...