Hello,
The MP300 uses one not rechargeable AAA battery, that will not be charged when connecting to the USB port of a computer.
When the player has abnormal behaviour, RESET the player as next:
1. Disconnect your player if it is connected to a
computer.
2. Remove the battery from the player. Wait 10
seconds, and then replace the battery.
3. Power ON the player, push the play/pauze/stop button >|| .
note
Check the correct polarity + and - of the battery matching the player.
Try a new battery when the RESET won't work.
To switch ON the player, press the play/pauze/stop button
>|| .
For switching OFF, press the
>|| button for at least 3 seconds.
There's a manual for the MP300 on this site:
http://www.cobyusa.com/files/manuals/MP300_MN.pdf : pdf files can be read with Adobe Reader.