Renault Scenic car will not start

somebody please help... almost 4 weeks ago my scenic broke down. the AA recovered me home, having identified a fuel pump problem. i took it to my local(and usually reliable) garage where they confirmed the fuel pump was just alive enough to feed the engine to idle. anyway long story short, i found a complete pump/sender unit and had it fitted, the car was feeding the fuel to the rails and still does, but, even though the engine turns over, it will not catch at all, it has only been attempted 5-6 times and the battery is already starting to drain as a result... could it be something so stupidly simple, or should i begin the search for a new car??????