AVEO 2007 Engine start problem

Engine start problem
Sometimes when my AVEO 2007 will start and run with no issue.. but when i turn of the key it wont start again.. fuel pump pressure is good, i tried feeding a gasoline into the intake manifold, the engine starts a few seconds, I was thinking it might be an injector issue, i took out the fuel injector and tried to start the engine. I notice that it is not injecting, not even one of the four injecot is injecting fuel mist. no fuel mist comming out from the fuel injector...I replace the camshaft sensor still thesame issue. It will start and when turned off it wont start again, can anybody help me. Thanks