89 Caravan won't start

Okay, basically. My van won't start. It's a 1989 Dode Caravan SE. I drove it all day and night. Stopped over at a friend's house for a few hours, went outisde to leave, and it wouldn't start. That was three days ago and hasn't started since. I'm confused because it was running perfectly fine the entire time before that. I've never had any problems until now. Mind you, it was like 20 degrees F out but it still won't start. Basically, I'm not too good at finding problems. I can fix them, but not find them. Does someone think they could list some possibilities (yes, I know that there are probably alot). But I have no money right now, and I can't work right now because I work out of my van. Help please!

Second option, does anyone know if the 89 Caravan has a self diagnostic test? If so, does someone know how to access it? I can't find any info online about it anywhere.

http://www.allpar.com/fix/80s-codes.html Read this and juny808's 19 Jan post.
I've got to hit the sack. Cheers.

All I was given was the starting code (12) and the ending code (55). Which I know means that the computer is reading anything that's wrong. I also happen to know/think that the computer can't read if the engine is misfiring. Let me give this info. The van has 155,000 miles on it. It's 12,000 overdue for an oil change and has never had a spark plug or spark plug wire change. That's my only idea right now. Any others? If I can't get this thing goin soon. I'm out of a job for sure and I'm gonna lose my place. Help would be greatly appreciated.

1 can only assume,recall the old ass out of u and me,that you have the 3.3 lit engine and if so I would be looking at the crank sensor( with out looking it up) you might also have a cam sensor.Square Crank's( Chrysler) was well known for the crank sensor just pullin the pin out of the blue.