I would treat it the usual. Wash with dishsoap and water and a brush. Then alcohol. Let it dry in the oven for an hour at lowest setting.
Careful visual inspection for anything off. Then see what happens when u plug it in. Note what any indicator leds are doing.
When it still doesnt work, i tend to start at the end and work back. Dc voltage at the terminals? Back to the voltage regulator. Then on to the (possibly very high voltage) power triac/fet thingies on the heatsinks. If they are broke, check whatever is driving the gate, cuz that is probably broke, too.
If u dont want to risk electrocution, just buy a new one. Drill holes in the bottom. Leave it in the rain. And see if it doesnt also break. ;]