Pages v5 does not store its preference files in the traditionally expected location. Copy/paste the following into the text input area of the dialog that results from pressing shift-command-G in the Finder, and then press return.
~/Library/Containers
Locate the com.apple.iWork.Pages icon (yellow). This is a package folder, so you will need to right-click on it and select Show Package Contents from the contextual menu.
Then, simply click the following folder hierarchy:
Data ▸ Library ▸ Preferences
Once you are in Preferences, just type Pages in the Finder's search window, and the com.apple.iWork.Pages.plist will be shown. Drag (move) that item to your Desktop. Press and hold the shift key when launching Pages again. Any change?