You don’t indicate which search engine you’re having an issue with. Google and Bing have respective webmaster tools to assist in determining issues.
Is the page part of the site internal link structure or external only?
If it is crawled and not showing up in the SERP’s, then you might have a quality issue or a penalty on that URL. Low-rank pages don’t necessarily show up in the SERPs. You can check to see if the page is in the Google index by searching site:yourdomain.com keyword or “phrase”. The results should show pages from your site that are in the index that match keyword or phrase. The omission of modifiers will show all pages indexed.