Before you disable the local Administrator account, make sure that there is at least one other local or network user who can gain access to the computer with administrator permissions. Otherwise, you will not be able to reverse this action in the future.
1. Log on as Administrator--> or as a user with administrator permissions.
2. Right-click My Computer--> and then click Manage.
3. In the left pane--> expand the Local Users and Groups--> and then click Users.
4. In the right pane--> double-click the Administrator account.
5. On the General tab--> select the Account is disabled check box--> and then click OK.
6. Quit the Computer Management console. The new setting takes effect the next time you attempt to log on to this computer.