If it's been rained on for several years, chances are the power supply has internal corrosion and the chip sockets on the mainboard will be oxidized and corroded. It may be salvageable by a good take-apart and cleanup, it may not. Since none of us can see the machine, we can't guess what the elements have done to it. If there's rust or white powdery stuff around the chips, that's not good. Check it out and let us know what you find.