First of all here is the apology from Prevx: http://www.prevx.com/blog/141/Windows-Black-Screen-Root-Cause.html

The issue is resolved by adding Explorer.exe to

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Shell=Explorer.exe 

If you encounter the Black Screen of Death, press ALT+CTRL+DEL 3 times and choose to open Task Manager.
Click the Applications tab.
Click New Task.
Click the Browse button and navigate to the Windows directory.
Click on explorer.exe, click Open.

Once Windows Explorer has loaded, open the registry editor and ensure that Explorer.exe is listed for Value Name Shell. If it's not, add it by right clicking on Shell and choosing Modify. Enter Explorer.exe in the Value Data field and click OK.