BleepingComputer.com: fryed mother board

I have a dell laptop, I fryed my motherboard from what I think was a bad adapter (It happened twice with the same adapter, but not with another one).

What exactly happens that frys a motherboard. The reason I am asking, is that dell laptop motherboards are very expensive, and I would like to restore one of my broken ones if possible. The symptoms that are displayed is that when the bad board is in the computer, when I push the power button, nothing happens, no lights, etc.

Rather then spending money on a new one, are the commonly fried parts replaceable. I guess what I am asking, and to equate it with an automobile, If you fry the battery cables, you don't replace the whole electrical system, just the bad cables. What should I look to replace in the broken board to make it work. Then again, it may not be possible.

Sometimes a bad part is obvious. Swollen capacitors, broken DC power jack, and sometimes you need specialized test equipment.
Then you need the specialized tools to remove/replace the parts. A soldering gun from Sears just won't cut it
Best thing you can do is to be pro-active
I don't believe in extended warranties, most of the time, but when you purchase a laptop. I definitely would