|Subject : Nissan Navara 1997 computer dead|
An integral part of the ECU is the immobilizer and anti theft system.
In order of rising cost possible fixes
Try a new key fob battery,
then a known good car battery,(check the terminals and terminal connectors, and all ground straps from the body to the battery,. and from the engine and gearbox to the body.
These models have a reputation for corroded ground points, and if you can see corrosion sneaking out of the ground cable at the terminations, replace the ground cables and grind the corrosion on the grounding points down to bare metal...electrickery requires a good ground return for the electronic signals that the computer relies on to regulate engine functions....
If all the above fails then have the ECU scanned for faults that may have been recorded by the system.
Google Fu using the query "1997 Navara/pathfinder won't start" gets multiple results e.g.