Mirrored Administrator Account

I have Windws Home Premium. About a month ago I installed updates for my
computer. But after the computer restarted there were two administrator
accounts. (when before there was just one) The accounts both have the same
user name and they both are administrator accounts. I don't think the extra
account is doing anything bad to the computer. But I would still like to have
just one account. Has anyone had this problem and how can I fix it.

P.S. It won't let me delete the account since the computer thinks its the
main account. And I reformatted my computer and there was only one account
but when I updated the same thing happened.