stem: im assuming you loosened the bolt on the top of the stem, and if when you did that its still stuck the first question is- is the head still sitting where it was, or as you loosened it, did it move up and away from the stem? if it moved away put a piece or wood or something on top of it and hit it with a hammer, it just means the wedge is jammed into the bottom of the stem.
if it doesnt move up as you loosen it, then the stem itself it seized into the head tube so thats just going to take some brute strength(penetrating oil) to get it out
headset:take it to a bike shop if you want to use it again...its possible to take it out with regular tools but u'll most likely mess it up if you don't have too much experience with bikes