What does the charging cable look like? I can't find one that seems to fit my Sansa....I've had it for 3-4 years.

I had the same problem with the P10 not charging via USB, I purchased mine second hand so it came with no charger. I assumed it would charge by the USB cable but it did not, the red light flashes but doesn't charge. Luckily I have an external battery charger for a different camera i got some years ago that takes a similar battery , the P10 battery didn't fit properly so I had to place it at a 45 degree angle into the charger making sure the outer contacts were lined up properly and taped it into place. After an hour it was fully charged and the camera is working fine. The charger is a 4.2 volt charger. New external chargers can be picked up on ebay cheaply

Look further than the batteries. Take the whole thing apart. That's what I do, and I've fixed a lot of things. And keep looking on the internet. A few hours of looking can result in years of listening.

this link may help there is a good section on replacing batteries and doing self test again

click here for manual

There are two possible problems:

1. the usb cable you are using is not working

2. the charge section of the Sansa is damaged.

does it start charging any at all, if it does then it could be a the charge section. If not it might be the cable. Try getting another cable to borrow that works or try using ur cable to charge another player, to see wat exactly is the problem.

The screws at the back of the sansa mp3 player can be taken out given u direct access to the battery, which can be taken out and charge with a universal charger. (be careful not to damage anything)

Buy it a new cable. Get one marked as USB 2.0
I have a ebook reader that was not charging via USB, the cable not fitting snugly.
I works fine with another cable, and, yes, it is a nice, snug fit.
The socket on the unit might be damaged or there may be a fault on the circuit board, but a loose connector is more likely.

You can download the manual from
http://www.sandisk.com/sandisk-support/warranty-and-user-guides

You can order the cable from
http://shop.sandisk.com/store/sdiskus/en_US/DisplayProductDetailsPage/parentCategoryID.11443000/CategoryID.11449200/productID.103565200

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.

I had the same problem this morning, albeit with my 8G Clip. Nothing worked -- the thing seemed dead as roadkill -- until I found a link about "forcing MSC mode." Basically, it told me to hold down the center button while plugging my Clip into my computer using my USB cable. Suddenly, boom! It's awake and alive and happy again. I'm unsure how that works, but that did it for me.

My best bet is the cable gone wrong. If you can find a similar cable to purchase from a computer shop or a friend you can try it.

This is direct from the sansa FAQs at http://www.sansa.com/support/sansa_clip/faqs 02. Why won’t my Sansa Clip charge when I connect it to my computer? USB Cable
Make sure that the USB cable is properly plugged in and use the original cable.

Computer in Hibernation mode
Make sure that the computer isn’t entering hibernate 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 your player is connected USB 2.0 port (1.1 occasionally causes charging problems).

USB Port location
Try plugging in different USB port (i.e. USB port in the back of the computer); sometimes the front USB ports have problem charging up the device.

Battery
Make sure the battery is fully charged. It takes approximately 3 hours to fully charge the battery.

Latest firmware
Make sure to update firmware by downloading and installing the Sansa Firmware Updater.

I hope this helps, and don't forget to rate the answer.