Re: How to Enable System Administrator

Enable Built-in Administrator Account
First you'll need to open a command prompt in administrator mode by
right-clicking and choosing "Run as administrator" (or use the
Ctrl+Shift+Enter shortcut from the search box)

Now type the following command:
net user administrator /active:yes

You should see a message that the command completed successfully. Log
out, and you'll now see the Administrator account as a choice.

You'll note that there's no password for this account, so if you want
to leave it enabled you should change the password.