AC815S inop. Amber light blinking 4 times and then shuts down

Plugged my ATT AC815s in to charge overnight and today it will not turn on. I press the "on" button and the LED blinks orange about 4 times and then shuts itself down. When I try to plug it in and turn it on, the initial sequence cycles over and over. I've taken the battery out, waited a while, and replaced it. Right now, the hotspot is a brick. Why?