Welp, All Darc has cursed me.
Wife came home and turned the TV on. She went to change the channel and the TV lost signal. Looks like the HDMI board has gone out, as the HTPC also isn't displaying. I've run component and RGA cables in the meantime to get TV back for the wife, but it isn't looking promising.
I bought this 60" plasma about 7 years ago for $1,000. Too soon for it to die, but I might have to replace it with a nice LCD
First I'll try removing the video board and reinstall it to see if it's just a loose connection. Next I'll try a solder reflow in the oven. If neither bring it back to life, I'll free it away on CL to someone who is OK with component only inputs.