I have the exact same login screen problem when my Lenovo W500 is docked with the lid closed and an external monitor with the same resolution connected via VGA. The boot screen shows on the external screen. After logging in the primary screen becomes the external screen.
1. boot your laptop with the lid closed and no external screen connected.
2. wait the normal amount of time it takes for the login screen to load.
3. connect an external screen.
Where is the login screen now?
I have noticed that if an external screen is connected at a later point then the login screen will show on the external screen in a decreased resolution.
I have learned to login to a blank screen