It happened to me again when I run the tablet down while traveling, and I fixed it immediately when I was back.
Here is the procedure to fix it
0. Accidentally run the tablet all the way down. (It powers itself off)
1. Connect the tablet to DC power and charge it for ~5 hours. The red LED should be on and flicker about twice a minute. Once the tablet is charged, the red LED is off when connected to DC power. Tablet is unable to turn on.
2. open the table, then connect DC power.
3. Short the GND pin of the regulator to system ground. (I used HDMI shield since it's close) see pic
4. The table should immediately turn on, let it boot up. WITH DC POWER PLUGING, restart the tablet multiple times. (I did it 5 times)
5. The tablet should be good to go.
The root cause of the problem appears to be when the battery is run all the down, the voltage is too low for the tablet to boot while charging. (I can see the red LED flicker when I was charging it.) And the repeated reboots, somehow accumulated charge in the ground pin of the key regulators and shuts it off.
*It may not be GND pin of a regulator, since I don't have the schematic. But its what it looks like to me.