There's only two things you need to check.. fuel and sparks.
Stick an old spark plug on the head (not the cover) so it's earthed. and connect one of the HT leads to it. When you crank the engine, it should be sparking.
If it doesn't.. try the others.
They should all spark. If one doesn't, it's the plug or the HT lead to the coil. If a pair don't, it's more likely to be the coil. If several don't... it's weird
but if all of them don't, then it's not the coils or plugs.. more likely the TDC sensor or the relay to the ECU.
If sparks look good, check the benzina. First of all, is there fuel being delivered to the injectors? Disconnect the petrol feed pipe from the pressure regulator and (catching the petrol in a rag or in an aerosol cap), get someone to crank the engine. No benzina means it's the fuel pump or the relays that activate it.
If there's benzina and sparks, you need to check if the injectors are squirting. Stick a bulb into one of the injector plugs (use one of those all-glass bulbs with the dangly metal loop tangs...) and see if it flashes when you crank the engine. If the injector doesn't have juice, check the others... If they all don't work it's a relay problem... If they all don't work and you don't have sparks either, then it's the TDC sensor.
Forget any other sensor or probe etc. They just make the engine run efficiently rather than whether it starts or not.
Also.. check the fuel shut-off switch under the front passenger seat.. Press it in if it's poking up.. and check that the fuel pump supply is flashing when you crank the engine.. If it doesn't it means the fuel pump relay is shagged or the shut-off switch isn't passing on the current, even if it's pressed in.
Don't give up though... sounds like just a dodgy connection somewhere or a duff TDC sensor..