Loss of activation for Office

I have now lost the activation for my Microsoft Office XP
professional, or at least it is saying that I am running
in reduced functionality mode that prevents me from using
the office products. I can re-activate it using the
Activate Product menu tool and it reports back that
office has an expiry NONE and Activity required NONE,
then moves me on to the next window that has only HELP and
EXIT buttons activated. The help refers me to the
subscription expiring on the activation, but a purchase it
as a package with the PC 5 months ago, as a once off
package, not a subscription service. Any answers any one,
it is not even asking for a CD to pick up the activation
so I am at a loss