[SwissXC90]

Start by checking battery voltage and putting a battery charger on it overnight if the battery is not fully charged.

Then the fastest easiest method is to use VIDA to read the codes and find out why the engine is refusing to start (but you may not have VIDA).

A no-start situation could be anything from a invalid key, the shiftlock preventing starter motor engagement, a failled startermotor relay, a failled startermotor, or many other things.

This is why reading the codes makes it so easy to diagnose. Without a code reader you are working blindfolded with your hands tied behind your back.