My girl friend just bought a Hawk 400 to learn on. It was running great and shifting just fine. We let it sit one day after riding for about 20 min, and now it will not shift. It will feel like it but it is not. I have checked the oil. The most I can get out of it is first,Neutral, and second it will come out of second by itself. Every other gear seems like it just in Neutral. Anyone with an idea?