1995 Ford Windstar Intake manifold

I recently replaced the intake manifold gaskets on my sisters ford winstar 3.8. I labeled everything good and didnt have any problems putting it back together. Only problem is.....it wont start. It turns over. I tried spraying starter fluid in the throttlebody but it still wouldnt even fire. I took it apart and double checked everything and everything seems to be hooked up properly. What could be causing this? Is there something stupid that Ive overlooked? Is there any common thing that one would over look twice?
thanks