my clio wont start?

Hi people, I'm new to this forum as Ive just started to have some trouble with my Clio... About a months ago I randomly started experiencing my clio not starting.that could be any time even after an hour of drive, if i stopped at work for 15 mins then it wont start back.

now last week it broke down, car wont start at all. it had fuel in there. then battry went flat by trying to start it. i think i made a mistake that left ignition on and tried to jump it so seen some sparks, so quickly switched engine off... there wasnt any apparent damage to ECU or battry.

RAC Turned up and since my clio is 1999 and V Reg he could not connect it to a computer to tell us the fault and said possible crank sensor so i replaced it next morning. but still wont start.

In Dash board warning lights, all others switch off apart from STOP.. garage i took too said there is no spark coming through plugs and also there is no fuel coming through fuel lines so its a possible ECU. but he is not sure and it is Trail n error on vehicle which is not a diagonostic really so even if i spen money on ECU it wont mean car is fixed. i suspected it is something to d with Immobiliser... it has remote central Locking and Imobiliser but i am not sure about the fault

Any Suggestions... i am desparate ....it is