Is the battery still in the device? If yes, that could be your problem. If no, then the problem is probably the charger cord needing replacing. However, please note, while you can run a laptop on the cord alone, you really shouldn't do it all the time. You should see about getting a new battery.
If getting a new cord, however, doesn't resolve the problem, you may well have fried the charging circuit, which would lead to possibly needing to replace the motherboard.