Engine will crank but not turn over

[Doyod]

Have a 2002 Altima S with 2.5L engine. Have had two recent no-start problems. First in September, 2013 was fixed with new crank position sensor, original cam position sensor unchanged. Second happened a couple weeks ago. Thinking I had the same problem as before, replaced the crank sensor again - no fix. Decided to also replace the cam sensor which had not been changed before, so two new sensors now in place, but still no fix. I'm pretty sure I'm hearing the fuel pump prime itself when I turn the key. Can anyone please tell me what I should be looking at next on either the fuel or ignition ends? Thanks for your help.

[ezb57e]

Pull out a coil and stick an old spark plug in it and ground the hex of the plug with a wire or touch ground.
Have someone try to start it and look for spark at the plug.
Use a stethoscope or just a long screwdriver and listen for ticking from the injectors while trying to start.
Listen to the fuel pump in a similar way.
Let us know what happens.