rough idle, now it won't fire up.

It was having a very rough idle when in park or in drive stopped at a light. when in neutral it was a lil more smooth but still not normal. The 03 lancer es i have sounds like its trying to start, the cams are turning over but it just won't start. I can't even get it to an autozone to have it scanned because it won't start now. anyone got ideas or have had similar problems to help me out? what should i do? i just replaced the radiator and thermostat so im not trying to spend hundreds of dollars until i figure out exactly whats causing this problem. btw the check engine light was cleared after the radiator was put in but then it came back on after about thirty- forty miles of driving

o2 sensor i think