Car won't start????

[niggy0]

I have just put my old ECU back on my car (as new one not arrived yet),
for some reason my car isn't starting - the starter motor goes but the engine won't kick in as if getting no fuel. Was just wondering if the ecu needs to be reset somehow for the transponder chip/immobiliser (after all this does work partly on the fuel pump).
if so anyone know how to do this / or what my problem may be (could it just be the fuel relay) - if so seems a strange coinsidence to go now.
Cheers all
Niggy0