The best thing to do if you find that your MP3 player has become frozen or stuck in one particular place is to attempt to power cycle it.
This can be done by powering the device off and waiting one minute before powering it back on.
It is important to note that prior to power cycling you should ensure that the device is unplugged and not charging or the device will be unable to complete the process.
If you find that this is unsuccessful on some players you can also try resetting the device. This can be done by simply inserting something like a paper clip or other fine pointed device into the reset slot on the top of the device.
Upon doing this you will be able to depress the reset button inside which will cause it to restart.