1997 golf gti 2.0 8v no spark comimg from coil lead???

my golf drives fine when it dose start.it always starts for first time in the day, but soon as i drive then turn it off again it dosnt start but its turning over?when i looked at the coil lead there was no spark so i changed the lead and coil but its still playing up?had it on test but no codes have come up coz every time i take it in the garage its starts every time!!!been told it sounds like the ecu or even the immobiliser? can anyone help me please,with an answer or hammer!! cheers steve