Engine won't start

Hello, it's impossible to tell from an online forum what went potentially wrong during parts replacement during a significant repair procedure on your Infiniti, or even if there are additional failures that occurred concurrent to your apparent head gasket concern. Questions I would ask: Why head gasket repair? Did you confirm a leak? Did you have the heads inspected when removed and serviced as needed at a machine shop that is highly skilled? Engine timing - no one here can see what you did or didn't do, but proper timing is a big concern. Are you getting spark and fuel and air at the engine when cranking now? This is not really a "do it yourself" repair, but if you've gone this far, you can address the questions I've asked and maybe come closer to an answer. Good luck.