Maybe you cause some damage to the soldering of one of the bga chips? Had a xserve g5 come to me recentley with a dead logicboard, but no outward signs of damage. the damage happened in shipping and the only thing i could think that could be at fault is that one of the bga chips had a weak connection and the shock of shipping managed to disconnect it. One day i will sit down and track down which chip is causing the problem with that board (the seller paid the cost of a replacement logicboard, so it's all good)

And since we seem to be sharing stories, last year i had a ipod classic come to me from one of my sisters friends, it's fair to say it had a very impressive amount of damage. It was in three pieces and every single metal piece of the ipod was bent (even the hdd had been bent into a U). I had to replace the back case, frame, hdd, battery and the headphone socket / lockswitch assembly. It also had had the battery connector knocked off the logicboard. After reassembly and having the ipod software restored to the new hdd it worked perfectly

I also had a fairly new laptop from him in similar condition, that didn't fare so well, the logicboard was bent and thus ruined