Ive been trying to charge my sansa and it wont charge..

Three possibilities;
1) You have a dead battery because the battery is no good.
2) You have a dead battery because your Sansa is no longer charging the battery.
3) You have a dead battery because you didn't leave your Sansa tethered long enough to charge it up.

When you have the Sansa c250 tethered to the computer, you should see a tiny yellow lightning bolt flashing, and a battery icon that shows the amount of charge on the battery.

If you see the lightning bolt, but the battery does not charge after being tethered to a working computer or charger for 24 hours, you may need a new battery. You can get one on Amazon.com. Here's a link:
http://www.amazon.com/HQRP-Replacement-Battery-Universal-Protector/dp/B001NZ981S

If you see the lightning bolt, and the battery charges after 24 hours, AND your player works when unplugged--Problem solved! You just need to let it charge for a longer time.

If you do not see the lightning bolt when the player is tethered, and the battery indicator shows "empty," It's likely that the internal plug to your Sansa c250 has broken. Your Sansa is no longer able to charge the battery.

If you happen to be an electrical engineer, or otherwise have a shop full of electronics equipment (including signal injector, volt-ohm meter, needle-tip soldering iron, and stereo magnifying goggles with work lamps) you may be able to fix it yourself. Otherwise, forget it-- your Sansa is dead.

If it's still under warranty, try to get it replaced. Failing that, it's time to get a new MP3 player.

Hope that helps! Please post a message to let others know what happened to your Sansa player.

Remove the back and check and see if the battery isn't fully connected

Below are some things to check for when charging your Sansa player:
USB Cable Make sure that the USB cable is properly plugged in and use the original cable that came with your player. Make sure the computer isn't entering hibernation or sleep mode while the device is connected. The computer must be ON in order to charge your player. USB Port 2.0 Make sure the player is connected to a USB 2.0 port (1.1 occasionally causes charging problems). USB Port location Try plugging into different USB ports (i.e. USB port in the back of the computer); occasionally the front USB ports have limited power to charge up the device. Battery Make sure the battery is fully charged. It takes approximately 3 hours to fully charge the battery. Latest firmware Depending on what Sansa player you have, make sure it's up to date with the latest firmware. AC charger (optional) AC chargers (sold separately) have a 500-1000 milliamp max output, which provides much better charging ability than a USB port. These accessories are available on our online store.
To Remove the Battery... 1. Remove the back on the e200 by removing the 4 screws. 2. Lift off the back by using a finger nail or a small flat head screw driver. It will not take a lot of force to remove. NOTE: When replacing the e200 battery be sure that the contacts on the battery line up with the contacts on the player. 3. The battery has three gold contacts on one end of the battery, which is near the words SanDisk Sansa. Be sure these contacts match up with the three gold contacts on the back of the player. 4. Lightly push the lined up battery up against the contacts of the player until the bottom end of the battery can be pushed into place. 5. Replace the lid to the back of the player and then plug the player into the computer using the Sansa cable. 6. Once the player has connected to the computer and is ready to be used or says "Connected", unplug the device.
NOTE: If the device goes directly to a black screen after unplugging it, then the battery has been replaced incorrectly. Take the back off the player once again and flip the battery around and the e200 device should work properly.

Hi it very much sounds like the on board batttery is not charged up, (not charging) hence when you plug into the PC it gets it supply from the USB 5Volts and plays as normal

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?

The battery may show "full' but still not hold a charge, so that when you unplug it from your computer, it goes dead. I assume you hold down the power button for several seconds and it still doesn't power up? Most likely, you battery is defective.

My friend give me a sansa mp3 player BB0703UBB. When i charge it in my PC and i forgot to unplug sansa mp3 player BB0703UBB after half hour i plug it. But the power is not working. i cannot open and play it anymore. I try to insert it on my PC but then it says unknown device. HELP!

Check the battery connection(s) in the back. Remove the 4 screws, remove the battery an re-connect it. Charge the device for a few hours. Best of Luck.

Dont turn it on and plug it in. That had happened to me and that fixed it.

Plug it into the computer (the cord you would use to charge it and transfer files), and hold down the power button for at least 15 seconds. The Sansa should then begin to turn on and start charging. :)