is this administrator account the inbuilt Vista account ?
OR
is it 'your' created account ?

if it is your created account, check it IS set as administrator [obvious, but we can miss things ]
as it is a 'home' edition, I don't know if your [local] computer managment will have a users and groups section, but if it DOES, check that your account is set into the admin group

don't forget to check at MS, mail them a question too
and they have a forum there too, that is pretty good at this sort of stuff

and, as always, please update the thread as and when you figure it out