My 605 runs fine without the keyboard or mouse, but requires I flip the switch on then back off then on again to boot (bad PRAM Battery).

Have you tried booting from a floppy with the HDD unplugged? See if it boots. Then I would try replacing the HDD (if you have a spare one) with a compatible System installed to see if it boots.

I do have to agree with uniserver, it sounds like it might be leaky caps.

PS: Be care around the wonderful Spindler Plastic.