On Windows Vista Business, Enterprise or Ultimate:
1. Click Start, type secpol.msc in the search box, then press Enter
2. From the list to the left, choose Local Policies, then Security Options
3. Set Accounts: Administrator account status to Enabled
4. Set User Account Control: Admin Approval Mode for the Built-in Administrator account to Disabled
 On Windows Vista Home Basic or Home Premium:
1. Click Start, type cmd in the search box, right click on the program cmd.exe and select Run as Administrator
2. In the command prompt window, type net users Administrator /active:yes then press Enter, you should receive a confirmation saying; The command completed successfully
3. Click Start, type regedit in the search box, then press Enter
4. Navigate to the section: [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System]
Double click FilterAdministratorToken and set it to 0
5. Next, logoff and you will see a new Administrator account is available. Login to this new Administrator account
Your now logged in to Windows Vista with full administrative rights.
You will not receive any security prompts like before and you should
have complete administrative rights to your machine.
