You have a short. My guess is that the rain had nothing to do with it. If you ever want to see your computer boot-up again, take it to your nearest Mac shop for professional repairs.
Well, I most certainly have heard of computers being damaged by power surges caused by lightning hitting power lines. In fact at the help-desk I worked at (which supports about 10,000 people) we'd get at least two computers a week written off by lightning strike.
If there is a strike pretty much anywhere between the nearest substation and your house, there is a pretty good chance the surge will be a lot more powerful than typical household surge protection can handle. Vulnerable items include computers, TV sets and for some reason refrigerators. For this reason, I always unplug when I see a really big storm coming in. A good insurance policy will cover that kind of damage, but you're better off not getting your computer toasted in the first place.
Of course, water is just as dangerous to a computer. Dmonto, is there any chance that rainwater could have come into the computer at all? If so, then it is most likely to damage the logic board and power supply, but with any luck nothing much else.