Can't sync music with iTunes?

Though I have successfully imported music to iTunes, iTunes failed to play them or failed to sync them to iOS devices like iPod, iPhone, iPad. How to solve such issue?

As we know, iTunes is not only a media player for playing music and movies, iTunes is also a media library application which helps to download, save, and organize digital audio and video and helps to transfer media files from computer to iPod, iPhone, iPad and Apple TV.
Firstly, you need to reinstall your iTunes. If it does not help, try to convert the music to standard mp3 format and try again. Bigasoft Audio Converter for MAC will help you convert all audio formats to mp3 for Apple device.

I think iTunes can help you to convert the audio file to mp3 format for iTunes and Apple devices.