There's two that could be the source of the problem. You'll have a crank position sensor and a cam position sensor. The CKP sensor is kind of behind the starter and is a little harder to get at. The cam sensor is a little easier. It should be on the front of the engine on the timing cover, driver's side, high up and they had a couple different models that do not interchange. If you need to replace it, double-check the build plate of the chassis to make sure that you have a 2004 and not a "leftover" 2003 because it was right around then that they made a switch.
First thing I'd check is to put the OBDII scanner on and turn the ignition to run to see if the ECU is alive. If you get response from the OBDII scantool, then the ECU is at least getting power. If it's not, then I'd start looking at fuses and relays.
You can test the sensors pretty easily since they're hall effect sensors which means they're basically pulsing an on-off voltage back to the PCM. The trick is that you need to pull the starter to get to and test the CKP sensor. I'd pull the connector off, turn the ignition to the run position, and then use a multimeter to see if you get +12V and -12V on two of the pins (I don't remember which is which, but I think - is the middle pin?). There's only three pins there, so it shouldn't take more than a minute to see if you're getting good voltage. If you're not, then the problem is upstream. I think it's a direct connection from the PCM through the harness to the sensor, so there could be a broken wire somewhere or the PCM itself could be the problem.
If you're getting good voltage, then you'd want to connect your multimeter black lead to the -12V pin that you already found and the red lead to the third wire through the back of the connector. Turn the engine by hand and see if your multimeter registers a voltage pulse as you turn the crank pulley. If you get on-off pulses, the sensor is probably good. If not, replace it.
There are OBDII codes for bad cam and crank sensors, but for whatever reason, they don't always get set even when the sensor is definitely bad.
