I currently spend most of my time on d2jsp in the computer hardware section, and i see alot of question get asked and then answered but people still are posting help after the issue has been resolved via pm or in the topic.
My suggestion is to add new button called New Question here

this will create a new create topic page that when it get published for everyone to see, the poster has the option on anyone that post to check their post as the correct answer (mod can even check the correct answer also), and in result it will display a new post saying their question has been answered by such and such, and close the topic. (or not depending if that would cause spam closing issues.) this would only be available in few forums, for example hardware forum and general help, and anywhere that question are commonly posted. i would do better explaining pictures for this but in class lol.