I've tinkered with my v3 and spilt water on it and it wouldnt turn on and I had to dry it really well before it could work. On my v4, the debug enables hyperspeed, but character selection doesnt work.
I had the same prob with my v3. Just open it up, and clean the buttons. On the circuit board that comes in contact with the buttons. Clean the gold connectors woth an eraser or something and make sure to get rid of the eraser dust afterwords :)