No power out from new 8400ATU

I've opened a ticket on this, but in the meantime, perhaps someone can point out my folly. I'm probably omitting something painfully obvious, but I am getting no power output from a new, out of the box 8400ATU which I just bought from FlexRadio as a “previously loved” factory reconditioned unit.

Because this is not my first Flex, SmartSDR 4.2.20 was already on my computer. When I hooked up the new 8400, the first thing it asked for was to update the radio from the previous version (which I presume was 4.2.18). So I updated the radio before doing anything else.

I'm connected to a dummy load (I've actually tried 2 different dummies). When I click on tune, the TUNE and MOX buttons light and the panadapter waterfall stops, but there is no indication on the TX meter, even if I slide the tune power up to 100%. This is consistent on all bands. I've performed a full reset (twice), but there is no change.

I plugged in the microphone, and the Level and Compression indicators dance in keeping with my voice, but there is no indication of power output in the TX window, even with the power slider at 100%. TX filters are set with Low Cut at 100 and High Cut at 3000. And yes, I am in band.