Um, a little more information, please. 1. Have you compared this keyword with other, similar keywords to see if this is a high number of searches? 2. Is it a short, one- or two-word phrase, or is it a longer phrase (long tail)? 3. Are you marketing to one local area, the nation, or the world? 4. How competitive is it?
You don't have to answer ME, but you do need to get the answers for yourself. Then you will have answered your own question.
If you are ranked #4 on Google for your keyword, with 12,000 searches per month, and you are not getting a response, you need to review your website ASAP.
Basic things to look at: 1. Is there an effective call to action? In other words, do you give people an easy way to buy? 2. Look at the writing of your website. Is it clear, concise, properly spelled, with excellent grammar and punctuation? 3. Are there links on your site? Do they all work? 4. Finally, look at your competition. What are they doing right and you are doing wrong?