Starting with Windows Vista, Microsoft decided to hide in mod default administrator account of the system, for security reasons. When we make a installation of a system Windows, besides the user account that we are asked to create it during the installation process (this will be the user that we will later use to log in to the system) are still created two additional accounts, both inactive (or hidden) default. One of the two additional accounts is user-ul Guest (which a user with administrator rights can activate for users who do not have acces permanent to the system, to prevent the installation of programs or Changing system settings by them) and the other is user-ul Administrator.
Desi Administrator account for systems Windows is not required to make changes in system settings or to apply certain restrictions (The user account created during the system installation process has Administrator privileges, the difference between that account and the default administrator account of the system is that the first is conditioned by UAC, while the last one does not receive the respective warnings), it is often or used for troubleshooting (system repair or of certain SETTINGS his).
If you are one of the users who have chosen to test the version Technical Preview of the operating system Windows 10 And you want to Activate the Default Administrator Account of this system, you can do this by following the instructions below.

How do we activate the hidden administrator account in Windows 10 Technical Preview?
Open one Command Prompt cu Administrator privileges (taste cmd in Start Menu or Start Screen, then click-right on the result Command promptly displayed and select Run as administrator)

In the open window type command net user And give Enter to display all user accounts of the system

Then, to Activate the Default Administrator Account, taste command net user administrator /active:yes (The same command you can use it and to Activate the Guest account, for example net user guest /active:yes)

If later you want to Disable again Default account of administrator, use the command (also in a prompt command with administrator privileges) net user administrator /active:no (The same command you can use it and to Disable Guest user or any other cont de user from the system; Just replace administrator cu the name of the user respectively).

Notes: If you do not need to be the default account of the Trobleshoting system, it is not recommended to activate and use this account. Compatible tutorial for previous versions of Windows (starting with Windows Vista).
STEALTH SETTINGS – How to enable the default Administrator account in Windows 10
 
			
For me this command did not work…Help me!