I will have to check it over and do more troubleshooting. The BGA solder crack issue just seems so likely. Here's the kicker... I brought it home, turned it on, and it worked for a long while until I removed the memory and reinstalled it. It's been intermittent since then. When I reinstalled the memory, I noticed that the logic board flexes an awful lot ... I figured that I might have cracked an already weak solder joint on the back side of the board, or something. There seems to be very little support directly behind the memory slots.