There is an aspect of duplicate questions I have long wondered about: I often see questions that are similar or identical to an existing question, but the answers to the older question are poor or incomplete in various ways. What is the right thing to do in such cases? Closing the question as a duplicate, or not asking it at all (if I am about to ask but discover a duplicate without a good answer) only serves to perpetuate the lack of a good answer.
Ask your question again. Link to the existing one, explain that the solutions there didn't help you, or that there are no solutions at all. Make sure your question is a better one than the dupe (more detailed, clearer, better researched, whatever) and then we can close the old one as a dupe of yours.
This situation is partially due to voting patterns. People don't like to downvote lousy answers, because doing so makes them look ungrateful (if only in their own eyes) and cost them rep. Add some sympathy upvotes and voila! - you have an upvoted answer which makes the question an eligible target for dupe closing.
So, if you're about to ask a question and have found a duplicate with a +1 answer which can't possibly help, just downvote that answer and ask. People won't be able to close your question if the dupe target doesn't have at least a half-decent answer:
Of course, this advice doesn't apply to cases where the answers in question are outdated or dealing with an issue which is not identical. In that case, @terdon's advice fully applies: you should be able to easily explain why your question is not a duplicate, so there's no problem to begin with.
Close as duplicate. If necessary, answer the existing question, edit it to improve the question (there's almost always room to do so!), or add a bounty to it.
If something got a lousy answer once, asking twice isn't going to magically make a better answer appear. Better to have everything consolidated so the voting system can work.
** Not an answer but I cannot add a comment with reputation < 50 **
As a reader of forums like this I get very frustrated with sites that kill a question as a duplicate - when google brought me to the 'killed' question.
Worst of all is when it gets closed with "answered elsewhere", but no reference. While, perhaps, that might have some relevance to whoever asked the question (do your research better) - it does not help someone who comes here later and does not know how your search mechanism works - to find that other better or worse question.
So, "reputation permitting" I am going to up-vote the answer that suggests to "duplicate-tag" the earlier question, especially if "new questions" get more weight from search engines.
Request to moderators: please ALWAYS add a link to the 'other', i.e. "not a dup" question. Many thanks!