If the derailleur moves, you haven't broken the derailleur or cable. If the derailleur moves but will not stay in place, it is not the derailleur's problem. There is an issue with your shift lever. When you "forced" it to shift you may have broken some of the internals in the shifter. At this point, your best course of action is to take it to a shop and have them look at it. It kind of sounds like you probably don't have the experience to diagnose/repair this problem yourself.