local admin account lost rights

The oddest thing. I log in as admin and have for quite some time. I
renamed the account over a year ago. I have virus updates weekly and upon
attempting to retrieve the latest patches from windows update was told I
must have admin permissions. Then I noticed I no longer have admin
permission to things like device manager or basic admin utilities, the
account has become a power user. Apparently there is no longer an admin
account. My firewall blocks all inbound connections and no users can install
any programs without verification from me first. I screen all inbound emails
as well. no attachments unless passed virus scanning first, further all .exe
files are stripped. I need to regain and admin account on this machine,
please help.