It depends on the severity. Sometimes, I change the viewpoint character or change the story I am working on to something as different as I can think of. Other times, I need to step away from the computer and take a few days to relax, as I ften get writer's block when I've been working extra hard on a story. I have found that, ore often than not, there is reason for the block. It may be that I am trying to write a scene from the wrong viewpoint, or that I am trying to push a character into an action which shouldn't occur. Once I work out what the issue is, I usually find the words start flowing again.