Windows: If you're having problems with a Windows 8 Store app, Microsoft offers a few troubleshooting tips and a utility that can automatically find and fix app problems for you.
Most of the time, the Windows Store will automatically tell you if there's a problem with an app and will try to fix it. However, some Microsoft support forum users are reporting Windows 8 errors such as failed Windows updates, and apps not working after upgrading from Windows 7.
Microsoft's troubleshooting advice include trying to update the app, sync its licence or reinstall it by going to Store > Settings > App updates to update or sync licences. To reinstall the app, swipe down on or right-click the app, and choose to uninstall it, then download it again from the Windows Store.
An easier automated option is to just grab Microsoft's Apps troubleshooter. When I ran it, the utility found some missing security settings I didn't even know about and automatically reset them for me.