The problem may not be related to the device. At first, I would try to reformat the SD card using a computer program as SD cards tend to get corrupted a lot of the time. Be sure to check out the Troubleshooting Page for more information.
One possibility could be that the device is not the problem here; the headphones you are using could also be at fault. Try using a different pair of headphones to see if the problem still persists. Be sure to check out the Troubleshooting page for more information.
The most common reason for this to occur is because the battery is done. The life of a battery was never designed to last for a long time, so there is a high chance that the battery needs to be replaced. A guide to the replacement of the battery can be found here. This could also be related to another problem with the device. Be sure to check out the Troubleshooting page for more information.