If a question does not have answer and somebody wants to ask the same question again , Will it be considered as duplicate ?
Yes, it will be considered a duplicate.
But you can edit the question, and add further details to it. When you edit the question, it will be at the top of the start page and others will see it.
If it still doesn't have any answer, you can add a bounty to it, and it will show up on the featured list.