A common troubleshooting step in many programs is to delete the "preference" file for an application that is acting up. This file (or files), which stores your user preferences, such as your preferred measurement system, color of your guides, etc., can be come corrupt and make the application unstable or behave strangely. When the file is deleted the application creates a new, fresh copy of the file.
To easily delete the preference file in InDesign, InCopy, Photoshop or Bridge, hold down command-option-shift-control (Macintosh) or control-alt-shift (Windows) immediately after you click the icon to launch the application. Keep holding the keys down until you see a dialog box asking you if you want to delete the preference file.