Starting on the logon screen, the shortcut Windows+ctrl+enter will work if it is set up, but not if it isn't. So if you try the shortcut on the logon screen and nothing happens, try this:
1. Press ctrl+escape to get to the start menu.
2. Type Windows+r (run)
3. Type "narrator" and press enter.
Once you have Narrator running, tinker with the settings. Be sure the 'use shortcut key' is checked. If you want narrator to start automatically on the logon screen, check that setting. There is also a setting to start Narrator automatically after logon, which can be checked.
The list of Narrator shortcut keys will display when you press capslock+f1.