Let's back up a little and think about this.
1. Before you changed the O2 sensor, the car ran fine correct?
2. After changing it, the white smoke and running rich began right?
3. At some point you had changed the plugs, was this before or after the car quit running?
4. Afterwards, it would crank but no fire (are the plugs wet?).
5. Now it acts like it won't crank right?
If everything I just listed is correct, the problem isn't the starter. Either your battery is low from all of the cranking or something is trying to hydrolock your cylinders (which would prevent the engine from spinning). If hydrolock is the case, something has caused your plugs to get wet in the process and started filling the cylinders.
It's a shot in the dark but what are the chances of your carb taking a dump? Does your oil smell like fuel and appear really watery?
I've also seen this happen with engines that have been WAAAY overfilled with oil. I bought a Malibu back in the day for $400 because the owner thought it had a bad head gasket. Seemed odd because it had a Goodwrench 305 in it. Turned out to have 3 gallons of oil in the engine. Changed the oil and the car ran great.
Just a few more possibilities to consider if you don't find a remedy anytime soon.