Renault Laguna car wont start

sounds like it needs a fuel leak off test
on top of all the injectors is a pressure leak off pipe in a garage we would connect a tube to the pipe and a cylinder to the tobe then crank engine if one of the cylinders fills up faster than the others it means the injector is stuck open.this can cause blue or black smoke and the car will not start.

My dads renault laguna 2.2dci intiale has a problem. It was fine up until about a week ago. He went to the petrol station and put some fuel in(diesel) and then came back to the car, and it wouldn't start. He tried this a few times and eventually it drained the battery. It turns over but won't actually start. Any ideas? He has had the AA out to it, but it won't come up on his computer. AA man seems to think it could be the crankshaft, my dad thinks its electrical. Has anyone had the same sort of problem? It sounds expensive whatever it is.