To enable administartaor account you can follow this steps
visit the Local Security policy, incidentally, this MMC is worth exploring in its own right.
This is how you navigate to the Local Security Policy.
Firstly click on Vista's Start orb, then in the Start Search dialog box type: secpol.msc. Note: you must include the .msc extension.
Secondly drill down to Local Policy, Security Options
Thirdly double click Accounts: Administrator account status and select enable.