Some Word2010 users reported an interesting issue:
You are viewing a document (with reviewing turned on) in Print Layout view, and after a few minutes, the view switches to Draft view and opens the comments window on the bottom. It usually happens when the computer is left idle for a
couple of minutes or sometime seconds.
Please verify EndNote X5 add-on is installed with Word2010. Try following methods:
1. Start in Word in safe mode (hold the CTRL key while starting word).
2. Disabled cite while you write - in endnote x5 tab, click the arrow on the bottom right of 'bibliography' -> instant formatting tab -> turn off.