Can you hard reset it? (I doubt but try)
What happened before becoming unresponsive? Have you flashed a wrong HWID firmware?Start with the device OFF and unplugged from power.
Touch and hold the lower right corner of the screen.
Continue touching and holding the lower right hand corner of the screen then power the device ON.
Release the power button when the device powers ON. You will see a new message: "Erase all user data?"
Remove your finger from the touch screen when this message displays.
If you cannot hard reset I doubt you can reach preboot mode.
Let us know.