Some Windows 7 users have reported a problem with the operating system that they were experiencing after installing the latest Microsoft security update on November 25 although there are some incidents where this problem seems to have been reported earlier than that. What happens is that the operating system will display a black desktop after startup with no options to interact with the operating system at this point.
Microsoft is currently investigating the issue. Good news though for users who have been experiencing the black screen of death after a Windows 7 update. Security company Prevx have released a fix for the issue. They do state that it will fix the most common cause for the issue which means that it will most likely fix the problem for most users but not for all.
Here are the instructions courtesy of Windows 7 News