A new WU update is available for Windows 10 Build 10061. The update KB3055415 fixes the Black Screen issue after login. Read the details below.
KB3055415 changelog:
This update fixes the following issue,
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.
