First does Office install at all -- doesn't have to be activated. Even if it doesn't run so long as it installs..
If it does then try running belarc advisor Belarc Advisor - Free Personal PC Audit
This should give you its product key which you can then either call ms to re-activate or re-enter the key on the office key screen and re-download.
(the program gives both the product key and serial number) so if you need phone re-activation then you should have all the data.
see screenshot -- even recognized I was running W8 CP !!!.