Sometimes we will need more details to troubleshoot, however here are 2 quick things to look at.
First, make sure that you have a default audio device selected for playback (you will see a small interface at the bottom left of the mixer. if it has a red circle with a line through it, it means you have no device selected)
Second, make sure there are no missing files or devices if you have move the original location of the song.
Third, make sure you have the proper permissions to read/write on the drive that the song is on.