If you can recall any of the song's lyrics, type them into a search engine.
Find the lyrics in an entry among the search results, probably a lyrics website such as songlyrics.com or azlyrics.com.
Click on the appropriate website, and find the song title listed above the lyrics.
If you could not find the title using the above steps, try going to an online resource, such as midomi.com/.
Follow the directions to hum or sing the song into your computer's microphone, and wait for the song to be identified for you.