Car not starting

Put key in the ignition and all electrical is working. Crank and no noise, none. Had someone give me a push and I jump started it, ran great. Thought it might have just been a fluke until it happened again. Jump started it again, fine. Now I have checked battery and connection, fuses and replaced clutch sensor (hope that is the correct term) and still nothing.
To clarify, when I say jump started I mean I popped the clutch while someone gave me a plush. Not that I use jumper cables to jump the car.