That's the first thing I would try, too. Also check your battery history (if you have any power). Does it indicate any charging activity at all, or only discharging? You can also try taking it in to a store that sells wireless Qi chargers and see if you can get it to respond to that.
Another possibility.. Has the device been dropped or tossed around by accident lately? Probably rare but in the event it has it could of broken or lost connection to the sealed battery inside.