It will not start

Hi, I live in Canary Islands, Spain. Here, like in the rest of Europe, Daihatsu has no longer any presence, including aftermarket and service.
My car has now started misbehaving and I do not know how to solve the issue because nobody is able to provide diagnostics due to the incompatibility of diagnostic software and vehicle motherboard.
The problem I am experiencing is the following. As I turn on he car, it stays on for about three seconds and then it switches off. I have been advised this could be an issue due to the keyhole not being able to read the key but after some tests this option has been ruled out. I also tested the sensors, which all seem to be okay. Another option which I thought about is the fuel pump not being able to work properly and as the fuel stream is blocked, the engine stops suddenly. The battery has been tested and it works fine.
The solution every mechanic suggests is to buy a new motherboard, but because nobody has the compatible software any longer, I am running the risk of one) not being able to configure the centraline and two) if the car brakes down again nobody will have a compatible diagnostics software and finally three) the cost of a new mother board is high, might as well buy a new car.
I would like to have more opinions on the matter before I am forced to buy another car as I cannot find any mechanic that can fix it.
Thanks in advance for your help, I look forward to reading the responses to my post.