Mac mini A1176 Not Booting

I have been given a "Late 2006" Mac mini 1.83 GHz Intel Core Duo that isn't booting. When you plug it into power, the DVD drive initializes and the front LED begins to blink continuously. From what I can tell from the Service Source guide, continuous blinking is meant to indicate that it is in "Power Saver" mode, rather than being a blink code for anything.

I disassembled and cleaned inside, re-seated the RAM and CPU, re-thermal pasted the CPU and GPU, and put it back together, but to no avail (not that I expected any of that to actually work, given the symptoms). Nothing looked obvious or alarming inside. Any suggestions? I do have a second, working unit of the same model that I can swap bits with to test things.

I did replace the coin cell (such BS that you have to completely disassemble the computer to remove it properly...)

I will try a PRAM reset, but presumably having a dead battery would be the equivalent, no?

I did test the hard drive outside the machine as well, and it mounts fine on another Mac.

The PSU is the one that came with it.