My mp3 when you plug it into the computer it says that the batterys fully charged.But when its unpluged from the computer and you try turning it on it says the batterys dead and shuts off

To charge the battery using your computer:
Connect iPod shuffle to a high-power USB port on your computer using the included iPod shuffle Dock. The computer must be turned on and not in sleep mode (some models of Macintosh can charge iPod shuffle while in sleep mode). When the battery is charging, the status light on iPod shuffle is orange. When the battery is fully charged, the status light turns green.
If you don't see the status light, iPod shuffle might not be connected to a high-power USB port. Try another USB port on your computer.

To charge the battery using an iPod USB Power Adapter If you do not have then you have to buy the same from Apple Store) 1 Connect the AC plug adapter to the power adapter (they might already be connected). 2 Plug the USB connector of the iPod shuffle Dock into the power adapter. 3 Plug the power adapter into a working electrical outlet. 4 Put iPod shuffle in the dock. You can disconnect and use iPod shuffle before it is fully charged.

Seems to be a charging/discharging issue for the battery. Try using the wall adapter only for charging and wait for it to fully charge before connecting to the computer or any other devices.

If you can turn your player on while being plugged to your PC/Laptop or USB charger, then your internal Lion battery is most likely gone past its useful life (some 500 charges or 18 months usage) and may need replacing. Most MP3 player may show 'fully charged' when plugged in either when the battery is truly fully charge or defective battery is no longer taking a charge: e.g. minimum or no current flow situation.

I plugged in my sandisc player to my computer to charge the battery and when I unplugged it fully charged it still just says connected?

If you have a phone charger with the same connector, plug in you Clip and leave it overnight. This will fully charge the battery. There is not enough power from the USB port.

Did you remove protective packaging on batteries?

Try another USB port on your computer that fixed the problem for me :) if not try on another computer.

That's because u didn't plugged in your computer. Your computer have to be turned on..

if you recharg it too much it could be wearing down, I'm guessing. unless oyu just got it.. you should take ti back because that's just messed

On my Colby player there is a small reset hole in the back. Mine has sometimes just stopped playing and shuts off. If you use a small wire (paperclip works well) push it in and reset it.