If you posted a question and it has gone unanswered, there are a few possible reasons:
1) Did you show your work? Homework helpers will not assist with any questions until you've shown your own effort on the problem. Remember, we
help with homework, we don't
do your homework. We already passed those classes; it's your turn to do so.

2) Did you include a descriptive title? Homework helpers often scan titles of threads to find questions they can help with. If you include the topic of your question in the title, it will get attention sooner than something that only says, "Please Help." Examples of good titles are, "Physics Kinematics Question" or "Biology Mitosis Question."
3) Have you given it enough time? Homework helpers are very busy, so may not be able to answer your question immediately. Please be patient.
4) We don't know how to help. Yes, it sometimes happens.

There may not be enough information provided, there may be a problem with the wording of the question, or it may be outside the expertise of the homework helpers who are online. This may be especially true for upper level (i.e., senior year) university coursework. If you are asking questions about upper level courses, it is a good idea to not wait until the last minute to post them. The more time you have, the more likely someone with sufficient expertise will find your question to help before your assignment is due.
If you are seeking help with problems that are giving you some heartburn, then you have come to the right place!
But if you are looking for someone to do your homework for you, then you have come to the
wrong place.
Please, for your own sake, try your homework before you come here, and show us where you got stuck. Speaking for myself and the other Mentors, Advisors, and Homework Helpers: We already know how to do your problem. Us doing it for you accomplishes nothing.
So, post away--and show your work!
Also, please DO NOT do someone's homework for them or post complete solutions to problems. Please give all the help you can, but DO NOT simply do the problem yourself and post the solution (at least not until the original poster has tried his/her very best).
Members who:
(1) attempt to get others to do their work for them, or
(2) post the same question in multiple forums, or
(3) prematurely post complete solutions to problems,
are violating the spirit (and policy) of PF!