Installation Issue
Re-installing everything was the only solution for Office 2007. In Office 2010 there is an alternative.
In Windows, go to the control panel and choose "Programs and Features". Select Microsoft Office 2010 from the list of installed applications and choose to change the installation. Once the installer is started, choose "Add or Remove Features". Then under "Office Tools" => "Actions Plugins" ensure "Bibliographic Information Actions Plugin" is set to "Run from My Computer". Then press "Continue" and let the installer run.
another option
Note that if you start in Safe mode, Word opens without a new blank
document. You will have to create it, for example by pressing Ctrl+N. Then
see if the commands are enabled on the ribbon.
If things do work OK in Safe mode, that indicates that there is a problem
with the Normal template, with an add-in, or with the registry. See also
http://us.generation-nt.com/redirect.html?url=http%3A%2F%2Fword.mvps.org%2FFAQs%2FAppErrors%2FProblemsStartingWord.htm.