If you installed Office and entered the key yourself, then Office didn't come pre-installed on your computer. If so, you must have bought it from a store. If so, it must have come in a Retail box. If so, then why can't you re-install it using the CD or DVD (that came in the retail box) and enter the product key (that also cam in the retail box)?
Thank you,
Darin Smith
WGA Forum Manager