: When you sign out of Windows 10 Technical Preview Build 10061 and return to the lock screen, you might see only a black screen with a responsive mouse cursor.
Pressing the Alt+Tab keys or the Ctrl+Alt+Del keys has no visible effect.
: At the black screen, press the Ctrl key once on an attached physical keyboard.
(You won’t see any visible change, but pressing the Ctrl key will place the cursor in the password box that you’re currently not able to see.)
Now type the password of the user that just signed out and press Enter.
This will sign you back into Windows and the desktop will appear.
If you failed to sign in because you mis-typed the password, press Enter once more.
Then retype the password and press Enter.