how can i make my car work (92 vauxhall cavalier 2.0 8v seh 4x4)?

it fires up but immediately shutsdown, its a petrol, started with basics then changed ecu, fuel pressure regulator, cam belt, timings ok spark plugs ,wiring loom, coil,vaf sensor, distributor cap, rotor arm, fuel pump ok, fuel flow ok, did some welding on inner wheel arch at front no wires damaged though, got clifford alarm with immobiliser (avantguard 5.5) and auto start wondering if it could have anything to do with that??? also checked fuses.