Music only plays for a second and then ends?
The most obvious explanation is that the file is incomplete: there's only a small fraction of the file there, or only the first section of the file is readable. Given that the symptoms you report in your other question point to SD card failure, that seems the most likely cause for this too.

If this is a different SD card, it could be that the card itself isn't at fault: rather, whatever you're using to copy files to the card could be corrupting the filesystem, or a dodgy USB connection to a card reader could be interrupting file transfers.