You are trying to install or update an app downloaded from the Windows Store, but it seems that the progress bar won't go beyond a certain point. Resetting the cache of the Windows Store can help to fix such issues. Windows 8.1 integrates a small utility allowing you to perform this task:
On the Startscreen, type: WSReset.exe. Right-click on WSReset.exe tool > Run as Administrator:
The Windows Store app will display a message indicating that the cache has been cleared:
All the traces of your activities (search, history...) performed on Windows Store will be deleted in the process.