I have a VW Polo Playa 1.4. I have replaced the pressure plate, flywheel, clutch cable of the car but unable to get clutch. The cable is pulling up the lever attached on the gearbox in order to shift gears but it does not shift, only when the car is switched off it does change gears. The pedal is connected to the cable so its not that, so what can be the problem?
as this is a mechanical linkage and not hydraulic it is likely that the cable (being new) needs to be adjusted up. Try that.
It sounds like the cable is out of adjustment, preventing the clutch pedal from disengaging the clutch plate from the flywheel. This would allow you to shift when the engine is off, but make it difficult to shift when the engine is running.
I would check to see if the cable is broken or binding anywhere. If not, follow these procedures (youtube link) for readjusting the clutch cable.