Car Started to smell and now won't start.

I was driving my 2001 Alero (4 cylinder) and there was a terrible smell like poo but car ran fine. I drove a couple of block and parked. A came back 2 hours later and the car would turn over but not start. Is it the passkey system? I originally thought it was the converter but it should start and then run and smell like crap. Any help would be appreciated.