When you have a post that not resolved and you go back, work on it, can you resubmit it if it is something you want to community look at before you submit it as your homework, or should you go back and edit the old post?
Always edit your original question instead of posting a new one if you haven't received any answers. If you received some answers but they didn't help, you can edit your original question to provide additional information. In general, editing the old question is preferred to posting a new one.
Every edit will "bump" the question to the front again as if it were freshly posted, so you will be able to get new eyes on your updated question.
Note that if you solved your problem on your own, you should post your solution as an answer to your own question. There's also a Code Review Stack Exchange site devoted to reviewing working code rather than fixing problems in it.
Please, do NOT edit your question for the sole purpose of "bumping" it. This is considered an abuse of the system.
If your question stinks, by all means do edit to improve. If you can edit to add a significant amount of detail which will help get you better answers, do so.
But if all you want is to get answers, we already have a method for attracting more users to your question, the bounty system.