1990 Isuzu Impulse Car wont turn over

Hi
I have a 1990 Isuzu Impulse. Car is in relatively good shape. I turned it on and was working one morning then it stalled while driving. I turned the ignition and can hear the engine as if it is going to start but the motor doesnt kick in. In the recent past, I replaced most of the major items such as the alternator, has new battery, starter etc etc. I was told once by someone that is could very well be the ECU though not sure how this would stop the car fron turning on? I did notice something strange if this help. There are two bottons between the driver and passenger duly called Econ/Manual. I have noticed that on the panel this its flashing Econ and Manual intermittingly. It has never done that before but its gone on for a a couple of weeks. I always had that button on Manual. Not sure if that could be the source.
I am not mechanically inclined but know the basics. Wondering if anyone can help me turn this car back on as its a great city car and nothing else. Please help