car suddenly wont start - never ran great anyway, esp. cold, now cranks, but won't st

[rjSupra]

Thanks Cre.

I hear you. That might not be a bad place to start. Also, for some reason I don't think my ECU is bad, just a hunch nothing more. But my O2 sensor looks pretty old and dirty on the outside, so I bet it's old and dirty on the inside too.
I wonder if the 02 sensor is so bad and dirty and old, and the temp was so cold here yesterday, maybe it just couldn't work (air temp in the teens, maybe lower). And maybe trying to start the car the 14 + times without it starting prompted my #21 error of ignitor / ignition pack failing to start after "A" times (which for my Turbo is 3 times in a row). So would that make sense?
Can a trashed O2 sensor cause some power issues by, what, messing up combustion or timing, and account for lowered power and crappy fuel mileage?
What do other folks get on their older Supras for MPG anyway? I think I read 14-30 mpg range. It would be very nice to solve this problem, have a running car, and a break from the headaches. I haven't even had time to think about the nasty PS leak with all the other stuff.