yamaha 4 stroke not starting

i have a 80hp yamaha efi 4 stroke 2005. was out yesterday engine was running fine then all of a sudden it started to lose power and surge then just died. turned key for a few seconds and it started up and ran again for a few minutes and doone the same thing . this happend everytime . i checked the batterys and the negative power cable was broke so i fixed it and the engine started again but after a few minutes done the same thing again. got home and conected water to the engine but this time it was very hard to start , after a few minutes i got it started it ran away for 10 minutes of so before i stoped again , now i cant get it to start at all it will turn over but it dont seem to be fireing. iv checked for fuel and all seems ok and is fresh fuel. checked fuses there fine. what could it be could it be after blowing the cdi if so how can i check. any help please. thanks

ok so i finnaly got her started.
under the hood were the big plug tat comes from the control box is theres a
conector thats has 4 wires goin at one side of it and 2 conectin to it.
i disconected this and after a few turns she fired up.
i thought i might be the kill switch conection but it dont seem to be as when i pulled the lanard off
the switch while this conector is diconected it still shuts the motor down.
any ideas what this conector is;

right so yesterday the engine ran fine all day , stop and start no probs.
now today i started the engine first turn and it fired up. the minutes later it chonked out.
when to restart and it back to not starting again.
somtimes it will start for a few seconds but then just stops , other times it doesnt start at all.
i pulled the injector rail off and turned the engine over but the injectors dont seem to be firing.
thers power at the injectors and i know they are ok as we tested them its almost like there not geting told to fire.
i should also state that theres good spark.
im really stuck here as i thought if it id the ecu surly the engine light would show on the tach.
please can somone help me out.
thanks
also i should state that even when the key is off after trying to start i seem to have 11.8v at the injectors.