I use a dirty trick.
I boot the machine to Linux, get into windows\system32, rename utilman.exe to utilman_old.exe, copy cmd.exe to utilman.exe then reboot to Windows.
Now you when you click on the accessibility icon on the Welcome screen, you get an admin command prompt.
This to add an account: net user admin 1234 /add
That creates a user account of admin with a password of 1234.
net localgroup administrators admin /add
That adds the admin account to the local administrators group
Reboot and login as admin, if you have full control you once again boot into Linux and undo the damage you did to utilman.exe, just delete the file and rename the _old.
This process works on all known versions of Windows.