Although by trying to switch it on you may have already damaged it, but for a non technical approach all you can do is to take the battery out and leave it sitting in a warm environment for about 48 hours, shaking it up and down / side to side every few hours to disperse any droplets of condensation that may have formed, if however after this procedure its still the same then you will have to seek out a proper service depot as there is no more you can do.