So when it is plugged into the wall, is there any light indicating that it is on AC source? There should be either a yellow or Orange LED that shows when AC is present. If there is not one, then check on the power convertor itself. There is ussually an LED on it, to indicate that it is in wall, it is green. Do you have a green light on it?
It sounds like the battery is completly drained, and the power cord is OPEN and not providing AC source.
Just some thoughts.