I'd say the next step should be to get the car plugged into a diagnostic device and pull off the fault code which should point towards the issue
1st check for spark by removing one of the spark plugs and plug it back into its lead andrest it on the metal of the engine ( DO NOT hold it on place by hand) then haveyour assistant turn the engine over whilst you watch the plug. It should give afat blue spark at regular intervals.
If not then checkthat there's power to the coil pack (at the other end of the plug lead) using a meter. If there’s 12V at the pack but no spark then check the ECU power supply(fuse and relay) and also the connections to the crankshaft speed sensor.
If there is a spark and its still not starting then its likely that the ECU isn't opening the fuelinjectors, if the injectors are working you can hear them click - its difficult to hear them with background noise so use a long screwdriver like a stethoscope, placing the handle end in your ear and the metal tip against the body of the injector whilst your assistant turns the engine over.
If you can't hear anything check the ECU power is present by measuring voltage at the fusebox and on its relay socket if OK then check the connections to the crank speed sensor and consider replacing this sensor if the wiring / connections look OK
If the car willstart using a squirt of quick/ easi start into the intake then this confirmsthe problem is lack of fuel
Also its worth checking that the electric pump that feeds the injectors is working correctly, it shouldrun for a few seconds then switch off when you first turn the ignition on. Ifyou remove the filler cap to the fuel tank and listen inside while your assistant flicks the ignition you should hear it clearly
If the connections to this are corroded or damaged then the pump could stop at any time. Checkthat its relay switches in and out and the relay contacts are clean and bright– replace the relay if in any doubt and do the same for the fuse, ideally measure the voltage at the pump and check its getting 12V.
You should be getting around 3 bar measured at the injector rail check to see if the plugs are getting wet indicating fuel is flowing – if not and the injectors are openingthen there’s a problem with the pump or the filter or even the pressureregulator
Could also be incorrect fuelling due to a faulty water temp sensor. If this isthe problem then the ECU will never add the 'cold start' extra fuel required if the car starts OK when warm then I 'd look into changing the sensor.