AirCard 815s won’t turn on

 I have an AirCard 815s that's going on 3 years old or so. It won't boot anymore. I plug it in and the ATT logo will come up and the status LED will run blue for a couple minutes as if it were booting normally. Then the LED will flicker amber and the screen will flick off for an instant before it seems to start booting again. After a few false starts, the screen shuts off, the status LED burns amber, and it will not respond in any way, regardless of what button I press. If I unplug and reconnect power (and battery) the cycle starts over.