the shitty immob has nothing to do with this, it acts solely on the fuel pump relay, using another key won't make a difference either, car doesn't care if its a key or a screwdriver smacked into the barrel.
Also the crap about the thing going on 2 or 3 cylinders, it doesn't have coil packs does it?
No thats right a coil and dizzy.
First remove the injectors power feed as its already flooded enough.
When you turn the ignition on does the tacho needle jump slightly? Does it move when cranking? if not then it could be the module or the CAS or TDC sensor as you lot like to call it although it doesn't actually detect TDC.
Get a multi meter on the crank sensors plug, you wan 230 - 270 ish ohms, if its open circuit then its fooked bang another in there.
Pull the coil lead off the dizzy, stick an old or a new plug into it and rest on the cam cover, crank it over, I very much doubt theres a spark. if there is though is it a bright blue one that gives off a 'crack' noise, if its yellow or sounds weak then we go to the...
ignition module, the coil is held to the module by 2 T20 screws, the coil pulls off, its connected to the module by wiper contacts which corrode, if they are corroded they can eventually arc and then no spark, clean them up as they will be corroded to some extent.
Done that and still no spark go get another module or swap with one from another car and plug it in see if it sparks then.
Also make sure the rotor arm or dizzy isn't cracked as it will then just track to earth.
When you get it sparking crank it over witht he throttle floored it will splutter a few times, when it stops spluttering then all the fuels out, plug the injector back in and fire it up.