I think we've all been there and I echo the suggestions to shoot something else. If you shoot landscapes, try shooting something completely different, even if it's not something you're passionate about. Try macro, product photography, cars, architecture, portraits, etc. What will happen is that you'll learn some new skills and they you'll be dying to try them out with landscapes.
Buying some good photography books can help as well. I have some Ansel Adams books that inspire me, and Genesis by Sebastiao Salgado is one I treated myself to last year. It's a stunning book and one that will inspire just about anyone.
Also... there is a book I liked... imagine by jonah leher... It discusses where creativity stems from in the brain and good ways to foster it... having said that... I'm not sure landscape photography lends itself to creativity.