How long will it take for a collection agency to report to the credit bureau?

[yelhsa4186]

OK,
I am new to this- it is my very first question, but I've decided I have to get answers because this problem is all I think about before I go to bed.
I was a student at a university in the fall of 2004, where I withdrew because of a medical condition. A year later a collections agency was calling me nonstop, at work, at home, leaving messages on my cell phone stating that I owed $13,000. I was 18 at the time and had no idea what to do. I was answering the phone calls and told them I know I needed to take care of this but that I didn't even finish the semester, but they didn't care.
About a month after they started calling my father passed away, i told them this, and they stopped calling. This was the last I ever heard from them. It is now two years since their last phone call or notification by mail, and nothing is on my credit report as of today!
I do not know what to do- Can they out of the blue sue me for this money?!? Why have they stopped contacting me period?
It wasn't a loan that I took out- it was for the tuition- it was a very messed up ordeal- I took a loan out in my own name and I asked for the complete $14,000 but it only stated the loan was for $1,000 after everything was completed. I was in school thinking I had a loan out for the entire semester- so I think it was the university that actually sent it to collections- And I have a loan for $1,000 that I don't have to pay until I graduate from the college I am attending now- and I think I should just pay that so i don't have any headaches, even though i didn't finish my semester there and I withdrew... what are your thoughts?