You said that this Stack Exchange web sites are question and answer sites, not help forums.
Yes that is true, BUT isn't the point people to be helped. Just btw this kind of questions might not help other but usually they will get similar errors and Google will point back to those stupid non-usable questions.
The point of the Stack Exchange network is people to be helped. So my proposal is that when a question "non-valuable", just add it some kind of badge "NON Valuable". Don't ban the user who asked.
Usually when you ask a question for something you don't understand you can't really make the question valuable for others.
Also there isn't a place where you can get help like Stack Overflow. It's the best way to ask a programming question and not to be answered a year after that.
So what is your opinion about this?