Let's say that I make a question and I get the solution through all comments.I get only one answer and did not solve the problem.Since I can't accept a comment as answer, should I accept the useless answer to increase my accept rate?
You should not accept useless answer.
If someone answer your question via comment, ask that commentator to convert his/her comment into an answer so that you can accept it.
If he/she does not reply you or does not make an answer, you can make an answer with linking those comments and make that answer CW because the question is solved by other. And accept it so feature visiting people also find the correct solutions.
I would not accept a useless answer just to increase your acceptance rate.
There are two ways that you can handle this:
First, if no one posts an answer that truly solved your question but you solved it using the comments, then I would post an the final solution that you came up with and accept your own answer.
You can use all of the information from the comments to post a final solution to your problem. Then at least your question will have been answered.
There is nothing wrong with answering your own answer even if you got their with the help of those commenting. You can even reference the comments in your answer so people know where you got the solution from.
Second, you can ask the person who commented giving you the solution to create an answer for you to accept.