Well, if it played for 3 minutes, it's NOT dead, clearly.
Those pins, unfortunately, are too easy to bend. It seems, however, if it was playing so recently and you haven't disconnected the boards, the pins must still be in the correct place.
With this in mind, all I can say is I think you should try using your hands to put a *little bit* of pressure on the boards near where the contacts are, to hold them together a little better, while powering on. Try that.
If that doesn't work, pull the B-board off, and check the pins again.