For the last 9 months or so it has not been unusual for me to end up at a black screen after an update. It occurs after logging on at the login screen. The mouse and keyboard are responsive and the mouse is visible but otherwise the screen is black.
Check the Windows Event Log, Dave.
In my experience this is usually caused by a Windows service failing to start (or taking too long). Windows Services are started sequentially, so if one hangs the next one cannot be started until the hung service times out (which can take up to 30 seconds). This can delay the appearance of the Windows Desktop and the result is a black screen where only the mouse pointer is visible.
Using the Event Viewer (Control Panel -> Administrative Tools) right after Windows startup you can identify the service causing the problems by looking at the time interval between events (normally there's a ton of entries all happening in very quick succession after logon, but if you find an interval between two events of several seconds, Bob's your uncle).
You can then either disable or delay the startup of the service causing problems (so the others can start first without interference). Here (Win7) the only problems I ever had of this kind were with the Razer services.
