My VW Polo will not start?

Please ignore my last question re VW Golf. I'm afraid the problem has really got to me. I don't know what car I have now let alone the day!!

I have a 1998 VW Polo 1.4L petrol engine that won't start but turns over OK. There is no petrol or ignition getting to the spark plugs. The fuel pump relay does not operate when I turn ignition key. I am getting +12V on 1 side of the coil but no earth on the other. The relay works if I put 12V across the coil contacts.
This earth comes from the ECU so I've repaced it for another from the breakers now but the condition still exists. Regarding the lack of a spark. I am getting 12V across the primary but zero on the HT lead. I was getting continuity across both windings but changed the coil anyway. Still no joy!
Could this be a immobiliser problem or a earthing problem or something else I've not considered?
Is there anyway of checking the immobiliser!