Well, if you have tried other chargers and it isn't working then either there is something on the tablet that is seriously using power and causing the drain (even when plugged in) or the battery is going.
To test if it is something on the device, try turning it completely off and then plug it in to charge. Does it charge? If yes, then there is something on the tablet. You would need to then find what is on it draining it so much. An app, malware, virus, etc. You may then want to try turning it off again, and restarting it in "Safe Mode". It should also charge just fine in "Safe Mode" if it is something on the device, which would not be able to run from "Safe Mode".
If none of that helps, and it still won't charge when turned off or...