In Windows 7 the admin or the administrator account is not active by default. If you want, you need to activate it manually (not recommended),
Why we need to activate admin account? Because, it may be necessary for making changes in system settings without having UAC or while performing a system troubleshooting you may need admin rights and privileges.
You can enable Admin account very easily with a run command or from the local policy. Here is how it is.
Enable Admin account: Click Orb button (Start button) and open command prompt with admin privileges (right click and select ‘run as administrator’).
Then run the following command: net user administrator /active:yes. [After executing the command, log off and log in your system.]
To Disable Admin account run the following command: net user administrator /active:no
Above is the very easiest method. You can also enable admin account from the local policy.
For that, type secpol.msc in the search box (Start – Search) and hit enter. Now navigate to Local Policies- Security Options – Accounts: Administrator account and double click the entry to enable or disable.
As said above, after doing this, log off and log in your system.