Could be any number of things really. Could even be something as simple as an earthing problem. Try getting a jumper lead and run it from the inlet to a strut tower and another from the earth terminal to the inlet.
I had this issue a few months back. Had poor earth to the motor so if and when it started it only run on 1 or 2 cylinders. Overcranking the motor trying to start it also fouled the plugs. I added two earth leads and a new set of plugs and never looked back now.