Edit: SirThinksTooMuch has a lot of good suggestions (I think). I just want to add that plot summeries are just to organise your thoughts on a story. You don't have to follow it point for point. If you believe that an event can be played differently than in your notes, go for it.
Try going for long walks. Note: I don't mean jogging, excercise, walks in the mall, because all those things can give too many distractions. I mean quiet walks along not too busy roads, preferably close to something to do with nature. Try to focus on your writing, where you want it to go, where you want it to start, what the characters are, what nuances they have, etc. Walking can be a very relaxing and produces chemicals in the brain that work against depression and anxiety, which can be a factor in the writers block. Not to mention its healthy. Get walkin'! If you've had any significant ideas after such a long walk, write them down when you get home, or you'll forget it. If possible, have a notebook with you and write your thoughts in it. And leave your iPod (if any) at home, since that's another distraction.
Reading stories in the genre of what you want to write can also help, especially darn good ones.
A more unorthodox approach is writing a fictional yet detailed review for your unwritten story. Essentially a very abstract form of making notes, by writing a long favourable review you can basically summerize the "look and feel" you want to achieve for a story, as well as your thematic goals (if any). It could also get your creative juices flowing in the right direction.
Edit: And you don't have to give it ratiings, because that would be silly. Reviews are not ratings.