99 won't start

I have had my 99 Sl for less than a month, two days ago it would crank but not start, it's like it's not getting fire or gas. The carlot I bought it from sent a salesman to my house by the time he got there I had it started, the code said my O2 sensor was slow delay, so I had the sensor replaced (carlot paid) but now it won't start again, after sitting for an hour it started, Help what can it be, it is my understanding, now that the O2 sensor probably didn't prevent it from starting in the first place. No indicator lights are on.