I had to redo the file associations and then I was able to open all Office files again. Figure this out by chance after scratching my head for the whole day yesterday. A Restore was not necessary. Unvelievable!"
If you have an OEM with a demo Office 2010 left on the box, you may have received an update for Office that is in turn making your system think it needs activation now. Go into programs and features and remove the trial version of Office or change the file associations.