I have a weird problem with my car.

its sat in the garage over winter and has developed a starting fault.

it cranks over fine but won't start (no spark, injectors or fuel pump). Jump it from another car thats running and it'll start straight away.

I've cleaned up all the battery terminals, tried a spare crank sensor, still the same. With the ignition on there is 5v at the map sensor so the ecu is getting power.

The only thing that makes sense to me is a relay somewhere sticking that switches when it gets the 14v from the other car but i dont know which one? I don't think its the ignition relay as wipers, lights etc still work ok.

Its also a bit intermittent as sometimes it will go without a jump but it cranks for longer than it normal before starting

Anyone got any ideas as I'm stumped and its doing my head in!