When you try to log on to a Windows 8.1-based or Windows Server 2012 R2-based computer, the logon screen turns black after you enter the credentials. Then, the computer becomes unresponsive.
Note The computer is unresponsive even if you press CTRL+ALT+DEL.
This issue occurs because an error occurs when the system tries to run the Userinit.exe process. Therefore, the Explorer.exe process cannot be started by the Userinit.exe process.
To resolve the issues, install update rollup 2887595. For more information about how to obtain this update rollup package, click the following article number to view the article in the Microsoft Knowledge Base:
2887595 Windows RT 8.1, Windows 8.1, and Windows Server 2012 R2 update rollup: November 2013
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:
824684 Description of the standard terminology that is used to describe Microsoft software updates