Another frequent complaint lately:
“I receive the following message when trying to open my email:
Cannot start Microsoft Office Outlook. Unable to open the Outlook window.
Could not open folders. No stores were found to be open.”

You need to reset the navigation pane to fix it. To do this, at the Start search field, Start menu, Run or Windows key + R, type:
outlook.exe /resetnavpane

See http://www.outlook-tips.net/beginner/switches.htm for more information on using switches.