Sure, I'll pile on. Connectors are also my guess. Not sure what you mean by "the game turns off" but if the MPU is sometimes booting and sometimes not that is most likely the reason. If time and energy is of the essence, I would start with repinning the SDB J3 connector. To help confirm this you might try lightly manipulating the J3 wires to see if you are able to help/hinder the MPU boot up.

And you certainly don't sound like a newbie, but ensure you do a really good job at repining. It is easy to let one pin make poor contact and not fix your problem and then you are really stumped.