All writers come to a point in their stories where the words just aren't coming. Normally you can walk away for an hour, a day, or a week until the words come back to you. You don't have that luxury during NaNoWriMo. So what do you do?
Paraphrase. Summarize. Make a list. When you get to that point in your story, the most important thing is to get the basic ideas down, whether it be a specific scene, an entire chapter, or speculative jottings about a character's motives. Yes, this will mean telling, not showing, but will also keep your word count building during the times when your story doesn't want to move forward. Eventually you will get back into your groove and your story will begin to flow again.