Dell D600 motherboard dead, Ac adapter dies when plugged in.

I have a Dell D600 and a few other motherboards that when I plug the ac adapter in the ac adapter dies then you have to unplug it to get it to reset. What Im looking for is what part on the motherboard is bad when this happens?? Also if anyone has a place to get the electrical plans for dell motherboards to help figure out the problem would be useful and appreciated. I see many boards like this and if I could fix it instead of having to spend 200.00 on a new one it would be great.
Thank You