2000 Pontiac Sunfire - randomly won't start

Hi Everyone, I have a 2000 pontiac sunfire that has about 103K miles. It has been randomly not starting for me (it will turn over but won't "catch") If I let it sit for 2 days it will start up again, run for a few days, then out of the blue will not start.
It does not have problems while I'm driving,just when I try to start it up. I have had it to 2 different shops and every time I have it towed it will start again for them :banghead:

Any ideas?

Air, fuel, fire.

If it won't start, check these. Air filter clear? Got fuel pressure? Got spark?

If you are 3 for 3, the spark timing is off.