Did you try charging the player using a cell phone charger? Perhaps your pc might not be putting out enough power to charge the player. If you are using a desktop pc you need to use a rear usb port, as the front ones are usually low power. If you are using a notebook, you need to plug the notebook in first before connecting the player to charge, as notebook usb ports typically revert to low power mode on battery power. Check the power saving options on your pc to make sure they aren’t cutting the power to the usb ports.
If your player won’t charge properly using a mini usb cell phone charger , then there might be something wrong with the player. If it is new then return it. If not and it is less than a year old, then rma it to Sandisk for replacement. It might be that the battery is defective or the battery wire disconnected.