Can you be more specific about how you are trying to open an image. Are you using the Organizer? Or are you double-clicking on a photo in Windows Explorer? Or are you using the File>Open menu in the Editor? (Or some other method?)
What happens when you do whatever it is you are doing? Are you getting any error messages?
Without knowing more, all I can suggest is that you try resetting the preferences file. Go to Edit>Preferences>General tab and click the Reset Preferences on next launch button.