Changed head gasket on renault clio 1.2 now wont start?

i changed the head gasket on a renault clio 1.2 d7f 720 engine and now it wont start it cranks over but doesnt fire it has fuel gettin to the injectors but no spark.

Any idea why it has no spark the coil is plugged in even if the leads were on the wrong way round it would still spark surely? i cant work it out

Hope you can help