i downloaded a song and it's not working

Hey there oki-kei,

It sounds like you are not able to play a song that you purchased and downloaded. I would delete the song one more time:

How to delete content you've downloaded from the iTunes Store, App Store, iBooks Store, or Mac App Store

http://support.apple.com/kb/HT5772

Mac or PC

1. Open iTunes.
2. From the Library pop-up menu, choose Music.
3. Click Songs in the navigation bar.
4. Click the song you want to delete.
5. Press Delete on your keyboard.

Then download it again from iTunes in the Cloud:

iTunes 11 for Windows: Download previous purchases from the iTunes Store

http://support.apple.com/kb/PH12491

Download previous iTunes Store purchases to an authorized computer

1. Click iTunes Store near the top of the iTunes window.
2. Click the Purchased link at the right of the iTunes Store homepage (below Quick Links).
3. In the page that appears, select a category.iTunes shows you which of your purchases are available for download. You can view all of your past purchases, or just the ones not currently in your iTunes library. Items already in your library aren’t available for download.If you select Music, you can view your purchases by song, artist, or album. If you’re viewing by album, click an album to see which songs on it are available for downloading.To search for an item, type its name or a keyword in the search field, and then press the Return key to view your search results.
4. To download an item, click its Download button .

Thank you for using Apple Support Communities.

Take care,

Sterling