I thought my Tekken 3 board took a dive. It had the exact same symptoms you have. Then I pressed the daughter boards together and she came alive again.
I reflowed the pins of pretty much all the chips on the daughterboard with no luck, then I read here about pressing the 2 boards together..
So I put a generous amount of IPA on both connectors, reseated the board and pressed them together.. and it booted right away.
And it continued booting after releasing them, not sure for how long it's going to continue booting
but at least I know where to look if that happens again.