iPod shuffle 4th generation plays a song repeatedly

Check the button position:

The top three way switch has three settings, on, continuous or shuffle. Green shading on the switch

indicates iPod shuffle is on, the next click over is continuous play, then the next tick after that should be shuffle.

Check the playlist:

It's possible you're stuck inside a specific playlist in the iPod, to change playlists you should be able to use the voiceover button. From the manual "Press and hold the VoiceOver ( ) button. Press Next/Fast-forward (‘) or Previous/Rewind (]) to move through the playlist menu. Press the VoiceOver ( ) button or Play/Pause (’) to select a playlist. Press and hold the VoiceOver ( ) button again to exit without making a selection."

Here's a pdf of the manual to help! Good luck!