no crank, no start?

i have been trying to get my car to crank for 2 weeks now and it has me stumped. It won't start and this led me to start trouble shooting possible reasons why I've replaced the starter, ignition switch, alternator and the oxy sensors both up and downstream. i hooked my autolink diagnostic too up to the OBD port and it doesn't give any error codes but it has a bunch of monitors that failed the initial testing during vehicle IM/readiness these were all centered around the exhaust system and catalytic converter to be specific.can u guys give me some insites into this most vexing issue...