Why isn't there any spark coming from the ignition coil on 1997 Mercury Villager GS?

I really need help on this one! I just don't get what the problem is. I just changed the head gasket and tried to start it back up and the next thing I notice there is no spark coming from the ignition coil (engine cranks and battery is fine). The timing belt and the setting is all fine. Its an 6 cylinder overhead camshaft engine. All the vac lines, fuses, seem fine.