This weekend I worked a bit on the system and finished recapping. The system will not power on using the MB button or keyboard. If I use a battery and short the pins on the PSU, it will turn on, chime and boot
Here it is booting, have the sound on for a treat. First time it has booted since 2000 (according to the most recent modified time on a file).
https://youtu.be/COLayTvlIQ0
The system will power off when I select Shut Down, or if I press the MB button. So I still need to figure why it won't turn on via the switch, but will power off.