When you open Regedit, it displays the last key you accessed in your previous session.
To stop this behavior, use Regedt32 to navigate to:
Double-click the LastKey value name in the right hand pane and clear the string. Press OK. Select the Regedit key and use Security / Permissions to remove or Deny Full Control from any user or group you wish. Press OK and exit Regedt32.
NOTE: If you don't wish to Deny access to this key, and you can't disable Full Control, you can always
just hold down SHIFT+LEFT ARROW to collapse the entries back to My Computer. I haven't found any problem (yet) with
denying myself access.