Some times I am asked to help with member servers where nobody any longer can remember the local administrator password.
In these situations I use an old trick.
Boot the system with your Windows CD, in this example we are working with Windows 2008 R2 and press SHIFT + F10.
Create a backup of the file C:WindowsSystem32sethc.exe
Now overwrite sethc.exe with cmd.exe
Exit the command prompt and restart the computer.
At the login screen press Shift quickly 5 times (try again if its not working the first time).
This will open Sticky Keys but also the command prompt.
Change the local administrator password with the command:
net user administrator NewPassword
Exit the command prompt.
Login to the system with the administrator account and your new password.
Finally remember to copy the backup of sethc.exe back again.
Instead of using SHIT + F10 at the boot screen this is an alternative way to the command prompt.
At the first screen when booting from CD select Next.
Select Repair your computer in the bottom of the screen.
Select your OS and click Next.
Select Command Prompt.
Now copy sethc.exe and backup as explained earlier, after exiting the command prompt select Restart.
The rest is the same as earlier.