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It should be plug and play. Check both ends of the connection, and the adapter. A few possible points of failure there. You may also want to have a USB keyboard to refresh the display if it's gone to sleep, and you may want to restart with the cable plugged in (but I suspect you may have tried to boot it a few times, although iirc some V2 units had a power issue with the HDMI being plugged in and a power cycle through unplugging / replugging power, so I would say try also plugging it in shortly after plugging in the power. You could see that issue with some LEDs on the board still illuminating from the HDMI plug when the power is out).