K. Scott Lewis
I use two methods. I open to a new page in my notebook and recreate the remaining outline from memory without going through old notes. This sometimes unhinges some blocks. If that doesn't work, I verbalize out loud how the plot would go if the heroes weren't there to stop the villain. Finally, if all else fails, I go run for 5 miles. Usually about mile 2 or 3 the ideas start flowing again.