It is likely that the battery is dead.
Clean the micro usb socket on the fone with an old toothbrush first.
Take the back off and remove the battery ... clean the battery contacts with an erasor.
Plug the fone into the charger, then put the battery in, and leave it to charge.
If it does not charge then first try another charger - the micoUSB charger is common to most fones (Samsung etc) other than crapple.
If the cleaning and trying another charger does not work then replace the battery.
The only other thing it could be is a damaged internal charge cct on the fone - this was the case with one of my HTC fones a while back.
Hopefully it is just a clean of the socket and battery, or a charger ... or lastly a new battery.