Megane Authentique 1.4

Help !!! I have a Renault Megane Authentique 1.4, 2001. The problem is that when I try to start the engine I have full electrics, but no responds from the engine. I have had a new alternator and battery. This happens about twice a week, and to get the car going again means bump starting it. PLEASE HELP ME.............. Before I go mad or the car goes over the nearest cliff. Thanks Wooliepigs.:banghead::confused:

you dont say if the starter motor is turning over - if it is check out the crankshaft sensor and engine control relay - andy