Most probable is the car charger has gone to full voltage and fried the PCB ower inout stage resulting in no charge, once the battery is depleted it won't start up, note the green LED will still illuminate but nothing gets through to power the unit up or charge the battery.
Second probable is a dead battery dragging the charger voltage down preventing the unit switching on, batteries can be changed with a little work, there is guide at the top of this forum section.
Take the back off the device and look at the PCB near the mini USB socket, do any components look fried? if not try a new battery, if fire damaged get a new unit and throw the old car charger away so it doesn't damage anything else - Mike