You'll want to enable the administrator account before doing this however, so that you are able to turn it back on again (there's a difference between an elevated account with administrative privileges, and the user account within the OS.
To do so, use the follow commands:
net user administrator /active:yes
net user administrator password *
The second command will then prompt you to set a password.
Thanxs @SixCoreFiend , i too stumbled on that link when i googled but was unable to reach there on PC , where can i find that "User Configuration\Administrative Templates\System" ?
Also it will take effect on the Guest account only or on all the accounts enabled ??