I asked about your stance width. If it is to narrow it could be causing you problems with your knee. Most people that are new to snowboarding ride a stance that is way to narrow.
Also you are complaining about your neck hurting when using proper form on a snowboard. Maybe you should try skiing so you don't have to worry about it. Or learn how to deal with pain, because if you continue to grow in the sport you a probably going to experience much worse.