You have to provide more info on this. Does it show a charge light? Pop out the battery for a few minutes and let it sit. I forget if the 3DS can power up at all (even with the charger connected) if the battery is bad but I don't think it will. If the charge light comes on then it may just need a new battery. If the charge light constantly blinks then it is probably the charger that has gone bad. Report back to see if there is anything else you can try.