My Renault Scenic seems to have an intemittant fault starting?

My 2001 1.6 Scenic started not starting every now and then a couple of weeks ago ,but when it wouldnt start if i left it for a bit and then tried a bit then it would sometimes fire.The immobilser light seems to be as normal and i swapped all the black relays around to see if this would highlight a knackered one.But now it wont start at all just turns over and over till battery dead.HELP