have you ran a fuel pressure test? or checked the AFM for opperation? If you have good fuel pressure unplug the wire harness from one of the injectors and hook up a test light to see if it is getting a signal from the ECU(the test light light will blink)

 

like the person said. fuel pressure test, do a pump test also, only other things i can think off (if your infact getting spark and compression) clean the injector filter.. not a easy job to do all 6 but its cheaper than buying new ones.
also make sure you dont have a crushed gas line or a leaky one..

last option, tow the car to a nissan dealer ship (where i work, i'll hook u up haha)

o one last thing that was wrong with my 280.. the injector pigtails (electrical connectors werent getting a very good connections..
if you have any more questions dont hesitate to contact me

 

i had that problem with mine as well all i did was change out the filter and it started right up with no hesitation..