With the engine cranking get a squirt can with motor oil in it and squirt oil along the edge of the manifold and gaskets you replaced see if oil gets sucked in. Ensure you have reconnected all electrical connections and hoses. Is there a Check engine light on once the engine starts and runs if so a scan tool will be required to retrieve the codes stored indicating where the problem is. You could try sparingly squirting carburetor cleaner into the intake manifold to see if the engine attempts to "fire" if it does you are lacking fuel, but I would first check for spark at the spark plug or ignition coil.