pathfinder cranks but won't start
 

HELP...does anyone have an idea as to why my 99.5 pathfinder won't start all of a sudden?
- fuel tank is full,
- fuel relay and and fuses look ok
- when key is turned 3/4 I can hear the fuel pump whine or a few seconds
- when key is turned, engine turns over very good but just doesn't start!!

When I tried to start over last two days....it started sometimes and other times not.
When I keep the peddle pressed down and then try to start....it seems like the engine is going to start but then it doesn't.

Any ideas.....fuel pump...distributor/rotor/wires ETC?