Found this online, hopefully if may be of some help. Apologies if you have tried this.
"If you are not able to access the settings menu (such as when the device hangs when updating), use Recovery mode:
If your device is on, hold the Power button to restart the device.
When the device turns off, press and hold the Volume Down button, then press and hold the Power button at the same time until the tablet turns on.
Press the Volume Down button twice to highlight Recovery mode.
Press the Power button to start Recovery mode. You'll see an image of an Android robot with a red exclamation mark and the words "No command."
While holding down the Power button, press the Volume Up button.
Use the volume buttons to scroll to "wipe cache partition" then press the Power button to select it.
When the cache is cleared, press the Power button on "reboot system now."