Disable UEFI Secure Boot.
Press and hold Volume-Up and Volume-Down, then power up or reboot the slate. It should go into BIOS setup.
In "Advanced Configuration", change "Attempt Secure Boot" to Disabled.
Press Volume-Up and Volume-Down to exit, then "Save Changes and Reset".
Power off the slate.
Plugin USB drive to slate. Press and Hold Volume-Up button, then power up the slate. It should boot into USB drive now.
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