I have a 1999 Buick century replaced upper and lower intake manifold. But now car won't start totally stumped

We're going to need some more information in order to assist from across the Internet.

How many miles on it?

Why were these replaced?

Does it turn over or not?

Does it turn over and not fire?

Does it turn over, fire, then quit?

Does it have spark?

What is the fuel pressure with the ignition on?

Did you do the work yourself or did you take it to a mechanic?

What is your mechanical skill level?

How many miles on it?

How many miles have you owned it?