User accounts nightmare!

I'm trying to enable the hidden Adminstrator user account by running CMD as admin and then 'net user administrator /active:yes'

but I always get the message 'system error 5 has occured. Access is denied.'

I have my own user account, I also have a guest account with administrator rights for some reason? but even when I log into the laptop under this guest user I still cannot run this script.

Any help will be very much appreciated as I seem to have hit a wall!

oh yeah - I forgot to say hello! :D