I had an issue where the jumper plug in the service box had a bad jumper wire connection. The machine would not turn on, wiggled them around and she turned on. Someones bad crimp job.
Quoted from andre060:
I'd move on to checking the 5V and seeing if the CPU is running. Start here: https://www.pinwiki.com/wiki/index.php?title=Williams_WPC#Power-On_LEDs_and_Sound_Tones_.28Bongs.29
At the test points was there any voltages.