Did it work before you changed the master cylinder? Does the cylinder have any pressure that can be felt to indicate it is moving the slave?
Also, make sure the salve bolts are all on the engine and they are tight. Several times I have had cars come in with one bolt that fell out, and the second one is either loose or broken. This allows the slave to move away from the engine when the clutch is depressed instead of disengaging the clutch.
Randy - RPM