Cranks will not start

The first step for this problem is always to have the diagnostic fault codes read and recorded. Many auto parts stores will do that for you for free if you can get the car there. The problem is their simple fault code readers usually only work on '96 and newer models. On '95 and older models, GM and Chrysler make reading fault codes yourself real easy. Yours is fairly complicated, but go to this page and give this a try:

https://www.2carpros.com/articles/nissan-obd1-diagnostic-trouble-codes-and-retrieval-procedure-1984-to-1994

We do not advise on bypassing system try another key first not a new one you can try our reset procedure or look online for a by pass by not a lot always work either. see link.
https://www.2carpros.com/articles/how-to-reset-a-security-system

There has to be something wrong with your testing. You need the exact fuel pressure. You also need to test for injector pulse using a noid light bulb.

The engine is it a GA-16DE?

Inspect the fuel filter at the firewall on the drivers side and also check the fuel pressure and comeback with the pressure readings.

If it starts every time you jump it, chances are that your battery is not holding charge. Use a battery charger to fully charge the battery (most auto store will do this for free) and no, leaving your car running for an hour will not charge the battery. Alternator is designed to replenish charge that you use in the course of starting the vehicle, not charging a discharged battery.

Is it a GA16DE or 2.0L Auto or Manual tranny

What do you mean by this: it just doesn't turn over.

Do you mean it doesn't crank over or it cranks and refuses to start I need this answered before I continue.

GA16DE

Check the fuse D 10amp
Inhibitor relay in relay box front left engine compartment
Or it could be the ignition switch

2.0L

Inhibitor switch at transmission also called the neutral safety switch.

Note: There's no starter relay for both.

Cheap tool get a remote starter find the starter circuit on the starter connect the clip to it and other to the battery cable on the starter-Push the button did the starter crank over. You need to answer this before we can proceed.

Have the battery and alternator load tested, then comeback

Diagnostic Trouble Codes - 1995
Nissan
11 Crankshaft Position Sensor
12 Air Flow Meter
13 Engine Coolant Temperature Sensor
14 Vehicle Speed Sensor
21 Ignition Signal
22 Fuel Pump
31 Engine Control Unit
32 EGR Function
33 Oxygen (O2) Sensor
34 Knock Sensor (Turbo Only)
35 EGR Temperature Sensor
43 Throttle Position Sensor
45 Injector Leak
51 Injector Circuit
54 A/T Control
55 No Faults In Memory

Get a starting fluid or ether and spray into the carb or the throttle body on an EFI. Did it start and die? If not disconnect a sparkplug wire or 2 and ground it to the engine -have helper crank engine over-do you have a snapping blue spark? If so-you have a fuel related problem, check the fuel pressure to rule out the fuel filter/fuel pump/pressure regulator and listen to the injector/s are they pulsing or hook up a noid light. No snapping blue spark continue to troubleshoot the ignition system-power input to the coil/coil packs, distributor pick-up coil, ignition control module, cam and crank sensors- Note: If it doesn't apply disregard it