#First
First check the master question and see if it solves your problem. What is the master question? Near the top of your question there will be what we call a "banner" pointing the the master question.
After looking over the answers to the master question, see if they solve your problem. If so great! Your question will now help point others to the correct answer.
#If not...
If the answers to the master question don't solve your problem, you'll need to get it re-opened. First, flag it for re-opening, explaining why your question isn't a duplicate. It also helps to edit your question to include why the master question doesn't solve your problem.
Last but not least, ask a question about it here on meta! It is perfectly acceptable to post a question here asking for your question to be re-opened. This is ususally the quickest way of getting it done, as users with 3,000 or more reputation can vote-to-reopen your question. It takes 5 votes to re-open a question, but moderators can always close and re-open a question on their own.
Once you have 250 reputation, you can view the amount of close or re-open votes your question has.