I logged in to a Windows Server 2008 VirtualBox VM as Abbas (local, standard-user account), ran cmd.exe as Administrator and then deactivated the Administrator through:
net user administrator /active:no
Please don't ask why I did that, I am still trying to figure out what the hell was I thinking. I have the administrator's password but I just can't figure out how to activate the account. Any suggestions, other then rebuilding the VM?