Check the following:

• If you can’t play a song purchased from the iTunes Store, you might have exceeded the number of computers on which you can listen to your purchases.

  Unless the song is an iTunes Plus version, you can play iTunes Store purchases on up to five computers. After you authorize five computers (by playing purchases on those computers), you can’t play purchases on a sixth computer until you deauthorize one of the five authorized computers. To deauthorize a computer, choose Store > Deauthorize Computer (the computer needs to be connected to the Internet), and then select “Deauthorize Computer for iTunes Store Account.”

  If the song is available as an iTunes Plus download, you can upgrade the song on the iTunes Store.

• If you’re listening to a shared library or playlist, iTunes skips iTunes Store purchases if this computer hasn’t been authorized to play them. To listen to a purchased song in a shared library or playlist, double-click the song. If your computer isn’t authorized to play songs purchased by the person who is sharing the song, you’ll need to enter that person’s Apple or AOL account ID and password to hear the song.

• You might be trying to play an AAC file that was not created using iTunes or downloaded from the iTunes Store. Songs you download from the iTunes Store or import into your library using the AAC encoder are encoded using the new MPEG-4 AAC format, and will play in iTunes and on your iPod. Older AAC files that you find on the Internet or elsewhere won’t play in iTunes.

• If you’re trying to play a song on a CD or DVD that you burned using iTunes, make sure the equipment on which you’re trying to play the CD or DVD is appropriate for the disc’s format. For example, if you burned a CD-RW disc, you can play it only on your computer and some newer CD players. If you burned an MP3 disc, it should work on your computer and on special MP3 CD players, but not on standard consumer audio CD players.

• Use Windows Update to make sure you have the latest Service Pack. Also check your computer or audio card manufacturer’s website to update your audio card drivers.

• If you’re having trouble playing music you’ve purchased from the iTunes Store, make sure you have the latest version of QuickTime.

• If you’re listening to a playlist that includes a song preview, the playlist stops after the song preview. Double-click the next song in the playlist to resume playing the remainder of the items in the playlist.

• If the song doesn’t sound right when you play it, you may need to change your QuickTime settings. Choose Start > Control Panel. Then double-click QuickTime and click the Audio tab. Click “Select Audio Playback and Recording Devices” and choose a different device. If the song still doesn’t sound right, try turning off the iTunes Sound Enhancer in the Playback pane of iTunes preferences. If that doesn’t work, visit the website below.