The stackoverflow engine has some stuff built into to it that will "bump" some questions. Also some rewards in the form of badges exist when you answer older questions.

If your question isn't answered, you should try to review it to see if you can improve it.

* Maybe your question wasn't clear enough.
* Maybe your question needed more background information, code, etc.
* Maybe your question had too much code example.
* Maybe your question was very hard and thus has not been answered yet.
* Maybe your question was lacking commitment on your part.

There are several ways of improving the answer rate for questions. This is a site where people answer questions because they want to, so you should have those people in mind when you ask a question.