Why won't it charge?

My dsixl turns on ok and runs fine, but it wont charge. When I plug in the wall charger the charge light does not go on. I thought that this might be a problem with the led, but a few seconds after I turn it on with it plugged in, it turns off because of a low battery, so it isnt charging because when I have it plugged in it works even with a low battery. I tried the charger in multiple outlets and tested the voltage output. There isnt a problem with the charger. Please help me.