Is this a small square MP3 player that you got from Asda for £25?
If so I have one just like it 😉
You need to the menu (press the return button a few times, the one next to play) go to the settings icon (looks like a flower, maybe, if you squint), press play, select play mode by pressing play, go down to "repeat all", press play, then press the return button to the top menu again, select music, then "play all".
Should work.
It keys the album and artist info off the "ID3" tag on the MP3 track by the way, not folder structure like your old one will off. Its actually quite good once you get the hang of it, well good for £25 anyway!
Oh – if its the same as mine you also want to change the screen saver to blank screen under settings, twice as much battery level!