Yes, I went through same issue and resolved it
check in add remove programs if you have 2 versions of Office installed e.g.
2007 and 2003 office. If yes you have 2 office installs, uninstall one office
version then activate the 1st install and validate it via
www.microsoft.com/genuine
then install the second install and activate it and validate it
Another cause: your Office was installed with a blocked Volume license
Product Key, for this you have to run Office genuine diagnostic tool to find
out if that is your issue
hope this helps!
Mathurin