You're absolutely right, it was working fine before I modded the powercord, erased the firmware, and installed a third-party hacked firmware on a ten year old drive

Any number of things could have gone wrong.
I will post a log when I get home today. My thought is that my probe is shorting the drive somehow, or caused a bad lead when I probed. I did miss the point a few times, but I never had any negative effects. It does seem strange that I can flash to LT+ just fine, but not to stock. That makes me think that my FW is incompatible--perhaps I should try the pre 02510 firmware when I get home as well.
Also, could it just be a laser/motor error causing the xbox to restart?