It is possibly more likely that the emergency update is in progress, but for some it isn’t that quick. I had this happen for the first time on my win7 netbook (which isn’t fast by any stretch of the imagination), black screen for ages.

If you get a black screen like this try using the old Ctrl+Alt+Del key combo and that will show you what is running in the background and give options. Once I saw that it was working and not dead, I left it to complete. I have never had this issue on my winXP system.

Ideally this shouldn’t be piggybacked onto this old topic but another more recent one or its own new topic.