If you are having trouble applying new themes, it’s entirely possible that you have to restart your Windows 8 themes service.
2. Now enter services.msc into the Metro search bar and hit Enter. This should come up, click on service.msc
3. A list with Windows 8 services will pop up, scroll down until you find the entry Themes
4. The Themes service is down the list, simply select it (blue) and then click on the blue Restart link to actually restart the service:
5. The service will now automatically restart. If you still have problems, you should check your graphic card drivers. As of right now there are some pre-release drivers available (official!) that you should install