Yup, it certainly was the power supply. I got a new supply with an increase in the power rating (not sure how I’ll spec this in the future), swapped it out in less than a half-hour, and voila — a working computer. Power supply swaps are easy, as long as the computer maker gives enough room to get to some of the connectors.
In my case, it was made a little tough by how HP placed the main 20-pin connector on the motherboard behind the drive bay. My big hands didn’t fit in there so well, so I had to pull the panel off the other side of the box, too, to get at it from behind.
But it works now, so I shouldn’t complain. Now, if the computer would just have the energy of my twins as they chant the mantra I want this computer to keep repeating…
The bouncing came from when they were watching a 70s music retrospective on PBS in our bedroom and decided they liked the phrase and could jump to the music.